Add ERT, a tool for automated testing in Emacs Lisp.

* Makefile.in, configure.in, doc/misc/Makefile.in, doc/misc/makefile.w32-in:
Add ERT.  Make "make check" run tests in test/automated.

* doc/misc/ert.texi, lisp/emacs-lisp/ert.el, lisp/emacs-lisp/ert-x.el:
New files.

* test/automated: New directory.

1 files changed, 2544 insertions, 0 deletions

diff --git a/lisp/emacs-lisp/ert.el b/lisp/emacs-lisp/ert.el
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+;;; ert.el --- Emacs Lisp Regression Testing
+
+;; Copyright (C) 2007, 2008, 2010, 2011 Free Software Foundation, Inc.
+
+;; Author: Christian Ohler <ohler@gnu.org>
+;; Keywords: lisp, tools
+
+;; This file is part of GNU Emacs.
+
+;; This program is free software: you can redistribute it and/or
+;; modify it under the terms of the GNU General Public License as
+;; published by the Free Software Foundation, either version 3 of the
+;; License, or (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful, but
+;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see `http://www.gnu.org/licenses/'.
+
+;;; Commentary:
+
+;; ERT is a tool for automated testing in Emacs Lisp.  Its main
+;; features are facilities for defining and running test cases and
+;; reporting the results as well as for debugging test failures
+;; interactively.
+;;
+;; The main entry points are `ert-deftest', which is similar to
+;; `defun' but defines a test, and `ert-run-tests-interactively',
+;; which runs tests and offers an interactive interface for inspecting
+;; results and debugging.  There is also
+;; `ert-run-tests-batch-and-exit' for non-interactive use.
+;;
+;; The body of `ert-deftest' forms resembles a function body, but the
+;; additional operators `should', `should-not' and `should-error' are
+;; available.  `should' is similar to cl's `assert', but signals a
+;; different error when its condition is violated that is caught and
+;; processed by ERT.  In addition, it analyzes its argument form and
+;; records information that helps debugging (`assert' tries to do
+;; something similar when its second argument SHOW-ARGS is true, but
+;; `should' is more sophisticated).  For information on `should-not'
+;; and `should-error', see their docstrings.
+;;
+;; See ERT's info manual as well as the docstrings for more details.
+;; To compile the manual, run `makeinfo ert.texinfo' in the ERT
+;; directory, then C-u M-x info ert.info in Emacs to view it.
+;;
+;; To see some examples of tests written in ERT, see its self-tests in
+;; ert-tests.el.  Some of these are tricky due to the bootstrapping
+;; problem of writing tests for a testing tool, others test simple
+;; functions and are straightforward.
+
+;;; Code:
+
+(eval-when-compile
+  (require 'cl))
+(require 'button)
+(require 'debug)
+(require 'easymenu)
+(require 'ewoc)
+(require 'find-func)
+(require 'help)
+
+
+;;; UI customization options.
+
+(defgroup ert ()
+  "ERT, the Emacs Lisp regression testing tool."
+  :prefix "ert-"
+  :group 'lisp)
+
+(defface ert-test-result-expected '((((class color) (background light))
+                                     :background "green1")
+                                    (((class color) (background dark))
+                                     :background "green3"))
+  "Face used for expected results in the ERT results buffer."
+  :group 'ert)
+
+(defface ert-test-result-unexpected '((((class color) (background light))
+                                       :background "red1")
+                                      (((class color) (background dark))
+                                       :background "red3"))
+  "Face used for unexpected results in the ERT results buffer."
+  :group 'ert)
+
+
+;;; Copies/reimplementations of cl functions.
+
+(defun ert--cl-do-remf (plist tag)
+  "Copy of `cl-do-remf'.  Modify PLIST by removing TAG."
+  (let ((p (cdr plist)))
+    (while (and (cdr p) (not (eq (car (cdr p)) tag))) (setq p (cdr (cdr p))))
+    (and (cdr p) (progn (setcdr p (cdr (cdr (cdr p)))) t))))
+
+(defun ert--remprop (sym tag)
+  "Copy of `cl-remprop'.  Modify SYM's plist by removing TAG."
+  (let ((plist (symbol-plist sym)))
+    (if (and plist (eq tag (car plist)))
+	(progn (setplist sym (cdr (cdr plist))) t)
+      (ert--cl-do-remf plist tag))))
+
+(defun ert--remove-if-not (ert-pred ert-list)
+  "A reimplementation of `remove-if-not'.
+
+ERT-PRED is a predicate, ERT-LIST is the input list."
+  (loop for ert-x in ert-list
+        if (funcall ert-pred ert-x)
+        collect ert-x))
+
+(defun ert--intersection (a b)
+  "A reimplementation of `intersection'.  Intersect the sets A and B.
+
+Elements are compared using `eql'."
+  (loop for x in a
+        if (memql x b)
+        collect x))
+
+(defun ert--set-difference (a b)
+  "A reimplementation of `set-difference'.  Subtract the set B from the set A.
+
+Elements are compared using `eql'."
+  (loop for x in a
+        unless (memql x b)
+        collect x))
+
+(defun ert--set-difference-eq (a b)
+  "A reimplementation of `set-difference'.  Subtract the set B from the set A.
+
+Elements are compared using `eq'."
+  (loop for x in a
+        unless (memq x b)
+        collect x))
+
+(defun ert--union (a b)
+  "A reimplementation of `union'.  Compute the union of the sets A and B.
+
+Elements are compared using `eql'."
+  (append a (ert--set-difference b a)))
+
+(eval-and-compile
+  (defvar ert--gensym-counter 0))
+
+(eval-and-compile
+  (defun ert--gensym (&optional prefix)
+    "Only allows string PREFIX, not compatible with CL."
+    (unless prefix (setq prefix "G"))
+    (make-symbol (format "%s%s"
+                         prefix
+                         (prog1 ert--gensym-counter
+                           (incf ert--gensym-counter))))))
+
+(defun ert--coerce-to-vector (x)
+  "Coerce X to a vector."
+  (when (char-table-p x) (error "Not supported"))
+  (if (vectorp x)
+      x
+    (vconcat x)))
+
+(defun* ert--remove* (x list &key key test)
+  "Does not support all the keywords of remove*."
+  (unless key (setq key #'identity))
+  (unless test (setq test #'eql))
+  (loop for y in list
+        unless (funcall test x (funcall key y))
+        collect y))
+
+(defun ert--string-position (c s)
+  "Return the position of the first occurrence of C in S, or nil if none."
+  (loop for i from 0
+        for x across s
+        when (eql x c) return i))
+
+(defun ert--mismatch (a b)
+  "Return index of first element that differs between A and B.
+
+Like `mismatch'.  Uses `equal' for comparison."
+  (cond ((or (listp a) (listp b))
+         (ert--mismatch (ert--coerce-to-vector a)
+                        (ert--coerce-to-vector b)))
+        ((> (length a) (length b))
+         (ert--mismatch b a))
+        (t
+         (let ((la (length a))
+               (lb (length b)))
+           (assert (arrayp a) t)
+           (assert (arrayp b) t)
+           (assert (<= la lb) t)
+           (loop for i below la
+                 when (not (equal (aref a i) (aref b i))) return i
+                 finally (return (if (/= la lb)
+                                     la
+                                   (assert (equal a b) t)
+                                   nil)))))))
+
+(defun ert--subseq (seq start &optional end)
+  "Return a subsequence of SEQ from START to END."
+  (when (char-table-p seq) (error "Not supported"))
+  (let ((vector (substring (ert--coerce-to-vector seq) start end)))
+    (etypecase seq
+      (vector vector)
+      (string (concat vector))
+      (list (append vector nil))
+      (bool-vector (loop with result = (make-bool-vector (length vector) nil)
+                         for i below (length vector) do
+                         (setf (aref result i) (aref vector i))
+                         finally (return result)))
+      (char-table (assert nil)))))
+
+(defun ert-equal-including-properties (a b)
+  "Return t if A and B have similar structure and contents.
+
+This is like `equal-including-properties' except that it compares
+the property values of text properties structurally (by
+recursing) rather than with `eq'.  Perhaps this is what
+`equal-including-properties' should do in the first place; see
+Emacs bug 6581 at URL `http://debbugs.gnu.org/cgi/bugreport.cgi?bug=6581'."
+  ;; This implementation is inefficient.  Rather than making it
+  ;; efficient, let's hope bug 6581 gets fixed so that we can delete
+  ;; it altogether.
+  (not (ert--explain-not-equal-including-properties a b)))
+
+
+;;; Defining and locating tests.
+
+;; The data structure that represents a test case.
+(defstruct ert-test
+  (name nil)
+  (documentation nil)
+  (body (assert nil))
+  (most-recent-result nil)
+  (expected-result-type ':passed)
+  (tags '()))
+
+(defun ert-test-boundp (symbol)
+  "Return non-nil if SYMBOL names a test."
+  (and (get symbol 'ert--test) t))
+
+(defun ert-get-test (symbol)
+  "If SYMBOL names a test, return that.  Signal an error otherwise."
+  (unless (ert-test-boundp symbol) (error "No test named `%S'" symbol))
+  (get symbol 'ert--test))
+
+(defun ert-set-test (symbol definition)
+  "Make SYMBOL name the test DEFINITION, and return DEFINITION."
+  (when (eq symbol 'nil)
+    ;; We disallow nil since `ert-test-at-point' and related functions
+    ;; want to return a test name, but also need an out-of-band value
+    ;; on failure.  Nil is the most natural out-of-band value; using 0
+    ;; or "" or signalling an error would be too awkward.
+    ;;
+    ;; Note that nil is still a valid value for the `name' slot in
+    ;; ert-test objects.  It designates an anonymous test.
+    (error "Attempt to define a test named nil"))
+  (put symbol 'ert--test definition)
+  definition)
+
+(defun ert-make-test-unbound (symbol)
+  "Make SYMBOL name no test.  Return SYMBOL."
+  (ert--remprop symbol 'ert--test)
+  symbol)
+
+(defun ert--parse-keys-and-body (keys-and-body)
+  "Split KEYS-AND-BODY into keyword-and-value pairs and the remaining body.
+
+KEYS-AND-BODY should have the form of a property list, with the
+exception that only keywords are permitted as keys and that the
+tail -- the body -- is a list of forms that does not start with a
+keyword.
+
+Returns a two-element list containing the keys-and-values plist
+and the body."
+  (let ((extracted-key-accu '())
+        (remaining keys-and-body))
+    (while (and (consp remaining) (keywordp (first remaining)))
+      (let ((keyword (pop remaining)))
+        (unless (consp remaining)
+          (error "Value expected after keyword %S in %S"
+                 keyword keys-and-body))
+        (when (assoc keyword extracted-key-accu)
+          (warn "Keyword %S appears more than once in %S" keyword
+                keys-and-body))
+        (push (cons keyword (pop remaining)) extracted-key-accu)))
+    (setq extracted-key-accu (nreverse extracted-key-accu))
+    (list (loop for (key . value) in extracted-key-accu
+                collect key
+                collect value)
+          remaining)))
+
+;;;###autoload
+(defmacro* ert-deftest (name () &body docstring-keys-and-body)
+  "Define NAME (a symbol) as a test.
+
+BODY is evaluated as a `progn' when the test is run.  It should
+signal a condition on failure or just return if the test passes.
+
+`should', `should-not' and `should-error' are useful for
+assertions in BODY.
+
+Use `ert' to run tests interactively.
+
+Tests that are expected to fail can be marked as such
+using :expected-result.  See `ert-test-result-type-p' for a
+description of valid values for RESULT-TYPE.
+
+\(fn NAME () [DOCSTRING] [:expected-result RESULT-TYPE] \
+\[:tags '(TAG...)] BODY...)"
+  (declare (debug (&define :name test
+                           name sexp [&optional stringp]
+			   [&rest keywordp sexp] def-body))
+           (doc-string 3)
+           (indent 2))
+  (let ((documentation nil)
+        (documentation-supplied-p nil))
+    (when (stringp (first docstring-keys-and-body))
+      (setq documentation (pop docstring-keys-and-body)
+            documentation-supplied-p t))
+    (destructuring-bind ((&key (expected-result nil expected-result-supplied-p)
+                               (tags nil tags-supplied-p))
+                         body)
+        (ert--parse-keys-and-body docstring-keys-and-body)
+      `(progn
+         (ert-set-test ',name
+                       (make-ert-test
+                        :name ',name
+                        ,@(when documentation-supplied-p
+                            `(:documentation ,documentation))
+                        ,@(when expected-result-supplied-p
+                            `(:expected-result-type ,expected-result))
+                        ,@(when tags-supplied-p
+                            `(:tags ,tags))
+                        :body (lambda () ,@body)))
+         ;; This hack allows `symbol-file' to associate `ert-deftest'
+         ;; forms with files, and therefore enables `find-function' to
+         ;; work with tests.  However, it leads to warnings in
+         ;; `unload-feature', which doesn't know how to undefine tests
+         ;; and has no mechanism for extension.
+         (push '(ert-deftest . ,name) current-load-list)
+         ',name))))
+
+;; We use these `put' forms in addition to the (declare (indent)) in
+;; the defmacro form since the `declare' alone does not lead to
+;; correct indentation before the .el/.elc file is loaded.
+;; Autoloading these `put' forms solves this.
+;;;###autoload
+(progn
+  ;; TODO(ohler): Figure out what these mean and make sure they are correct.
+  (put 'ert-deftest 'lisp-indent-function 2)
+  (put 'ert-info 'lisp-indent-function 1))
+
+(defvar ert--find-test-regexp
+  (concat "^\\s-*(ert-deftest"
+          find-function-space-re
+          "%s\\(\\s-\\|$\\)")
+  "The regexp the `find-function' mechanisms use for finding test definitions.")
+
+
+(put 'ert-test-failed 'error-conditions '(error ert-test-failed))
+(put 'ert-test-failed 'error-message "Test failed")
+
+(defun ert-pass ()
+  "Terminate the current test and mark it passed.  Does not return."
+  (throw 'ert--pass nil))
+
+(defun ert-fail (data)
+  "Terminate the current test and mark it failed.  Does not return.
+DATA is displayed to the user and should state the reason of the failure."
+  (signal 'ert-test-failed (list data)))
+
+
+;;; The `should' macros.
+
+(defvar ert--should-execution-observer nil)
+
+(defun ert--signal-should-execution (form-description)
+  "Tell the current `should' form observer (if any) about FORM-DESCRIPTION."
+  (when ert--should-execution-observer
+    (funcall ert--should-execution-observer form-description)))
+
+(defun ert--special-operator-p (thing)
+  "Return non-nil if THING is a symbol naming a special operator."
+  (and (symbolp thing)
+       (let ((definition (indirect-function thing t)))
+         (and (subrp definition)
+              (eql (cdr (subr-arity definition)) 'unevalled)))))
+
+(defun ert--expand-should-1 (whole form inner-expander)
+  "Helper function for the `should' macro and its variants."
+  (let ((form
+         ;; If `cl-macroexpand' isn't bound, the code that we're
+         ;; compiling doesn't depend on cl and thus doesn't need an
+         ;; environment arg for `macroexpand'.
+         (if (fboundp 'cl-macroexpand)
+             ;; Suppress warning about run-time call to cl funtion: we
+             ;; only call it if it's fboundp.
+             (with-no-warnings
+               (cl-macroexpand form (and (boundp 'cl-macro-environment)
+                                         cl-macro-environment)))
+           (macroexpand form))))
+    (cond
+     ((or (atom form) (ert--special-operator-p (car form)))
+      (let ((value (ert--gensym "value-")))
+        `(let ((,value (ert--gensym "ert-form-evaluation-aborted-")))
+           ,(funcall inner-expander
+                     `(setq ,value ,form)
+                     `(list ',whole :form ',form :value ,value)
+                     value)
+           ,value)))
+     (t
+      (let ((fn-name (car form))
+            (arg-forms (cdr form)))
+        (assert (or (symbolp fn-name)
+                    (and (consp fn-name)
+                         (eql (car fn-name) 'lambda)
+                         (listp (cdr fn-name)))))
+        (let ((fn (ert--gensym "fn-"))
+              (args (ert--gensym "args-"))
+              (value (ert--gensym "value-"))
+              (default-value (ert--gensym "ert-form-evaluation-aborted-")))
+          `(let ((,fn (function ,fn-name))
+                 (,args (list ,@arg-forms)))
+             (let ((,value ',default-value))
+               ,(funcall inner-expander
+                         `(setq ,value (apply ,fn ,args))
+                         `(nconc (list ',whole)
+                                 (list :form `(,,fn ,@,args))
+                                 (unless (eql ,value ',default-value)
+                                   (list :value ,value))
+                                 (let ((-explainer-
+                                        (and (symbolp ',fn-name)
+                                             (get ',fn-name 'ert-explainer))))
+                                   (when -explainer-
+                                     (list :explanation
+                                           (apply -explainer- ,args)))))
+                         value)
+               ,value))))))))
+
+(defun ert--expand-should (whole form inner-expander)
+  "Helper function for the `should' macro and its variants.
+
+Analyzes FORM and returns an expression that has the same
+semantics under evaluation but records additional debugging
+information.
+
+INNER-EXPANDER should be a function and is called with two
+arguments: INNER-FORM and FORM-DESCRIPTION-FORM, where INNER-FORM
+is an expression equivalent to FORM, and FORM-DESCRIPTION-FORM is
+an expression that returns a description of FORM.  INNER-EXPANDER
+should return code that calls INNER-FORM and performs the checks
+and error signalling specific to the particular variant of
+`should'.  The code that INNER-EXPANDER returns must not call
+FORM-DESCRIPTION-FORM before it has called INNER-FORM."
+  (lexical-let ((inner-expander inner-expander))
+    (ert--expand-should-1
+     whole form
+     (lambda (inner-form form-description-form value-var)
+       (let ((form-description (ert--gensym "form-description-")))
+         `(let (,form-description)
+            ,(funcall inner-expander
+                      `(unwind-protect
+                           ,inner-form
+                         (setq ,form-description ,form-description-form)
+                         (ert--signal-should-execution ,form-description))
+                      `,form-description
+                      value-var)))))))
+
+(defmacro* should (form)
+  "Evaluate FORM.  If it returns nil, abort the current test as failed.
+
+Returns the value of FORM."
+  (ert--expand-should `(should ,form) form
+                      (lambda (inner-form form-description-form value-var)
+                        `(unless ,inner-form
+                           (ert-fail ,form-description-form)))))
+
+(defmacro* should-not (form)
+  "Evaluate FORM.  If it returns non-nil, abort the current test as failed.
+
+Returns nil."
+  (ert--expand-should `(should-not ,form) form
+                      (lambda (inner-form form-description-form value-var)
+                        `(unless (not ,inner-form)
+                           (ert-fail ,form-description-form)))))
+
+(defun ert--should-error-handle-error (form-description-fn
+                                       condition type exclude-subtypes)
+  "Helper function for `should-error'.
+
+Determines whether CONDITION matches TYPE and EXCLUDE-SUBTYPES,
+and aborts the current test as failed if it doesn't."
+  (let ((signalled-conditions (get (car condition) 'error-conditions))
+        (handled-conditions (etypecase type
+                              (list type)
+                              (symbol (list type)))))
+    (assert signalled-conditions)
+    (unless (ert--intersection signalled-conditions handled-conditions)
+      (ert-fail (append
+                 (funcall form-description-fn)
+                 (list
+                  :condition condition
+                  :fail-reason (concat "the error signalled did not"
+                                       " have the expected type")))))
+    (when exclude-subtypes
+      (unless (member (car condition) handled-conditions)
+        (ert-fail (append
+                   (funcall form-description-fn)
+                   (list
+                    :condition condition
+                    :fail-reason (concat "the error signalled was a subtype"
+                                         " of the expected type"))))))))
+
+;; FIXME: The expansion will evaluate the keyword args (if any) in
+;; nonstandard order.
+(defmacro* should-error (form &rest keys &key type exclude-subtypes)
+  "Evaluate FORM and check that it signals an error.
+
+The error signalled needs to match TYPE.  TYPE should be a list
+of condition names.  (It can also be a non-nil symbol, which is
+equivalent to a singleton list containing that symbol.)  If
+EXCLUDE-SUBTYPES is nil, the error matches TYPE if one of its
+condition names is an element of TYPE.  If EXCLUDE-SUBTYPES is
+non-nil, the error matches TYPE if it is an element of TYPE.
+
+If the error matches, returns (ERROR-SYMBOL . DATA) from the
+error.  If not, or if no error was signalled, abort the test as
+failed."
+  (unless type (setq type ''error))
+  (ert--expand-should
+   `(should-error ,form ,@keys)
+   form
+   (lambda (inner-form form-description-form value-var)
+     (let ((errorp (ert--gensym "errorp"))
+           (form-description-fn (ert--gensym "form-description-fn-")))
+       `(let ((,errorp nil)
+              (,form-description-fn (lambda () ,form-description-form)))
+          (condition-case -condition-
+              ,inner-form
+            ;; We can't use ,type here because we want to evaluate it.
+            (error
+             (setq ,errorp t)
+             (ert--should-error-handle-error ,form-description-fn
+                                             -condition-
+                                             ,type ,exclude-subtypes)
+             (setq ,value-var -condition-)))
+          (unless ,errorp
+            (ert-fail (append
+                       (funcall ,form-description-fn)
+                       (list
+                        :fail-reason "did not signal an error")))))))))
+
+
+;;; Explanation of `should' failures.
+
+;; TODO(ohler): Rework explanations so that they are displayed in a
+;; similar way to `ert-info' messages; in particular, allow text
+;; buttons in explanations that give more detail or open an ediff
+;; buffer.  Perhaps explanations should be reported through `ert-info'
+;; rather than as part of the condition.
+
+(defun ert--proper-list-p (x)
+  "Return non-nil if X is a proper list, nil otherwise."
+  (loop
+   for firstp = t then nil
+   for fast = x then (cddr fast)
+   for slow = x then (cdr slow) do
+   (when (null fast) (return t))
+   (when (not (consp fast)) (return nil))
+   (when (null (cdr fast)) (return t))
+   (when (not (consp (cdr fast))) (return nil))
+   (when (and (not firstp) (eq fast slow)) (return nil))))
+
+(defun ert--explain-format-atom (x)
+  "Format the atom X for `ert--explain-not-equal'."
+  (typecase x
+    (fixnum (list x (format "#x%x" x) (format "?%c" x)))
+    (t x)))
+
+(defun ert--explain-not-equal (a b)
+  "Explainer function for `equal'.
+
+Returns a programmer-readable explanation of why A and B are not
+`equal', or nil if they are."
+  (if (not (equal (type-of a) (type-of b)))
+      `(different-types ,a ,b)
+    (etypecase a
+      (cons
+       (let ((a-proper-p (ert--proper-list-p a))
+             (b-proper-p (ert--proper-list-p b)))
+         (if (not (eql (not a-proper-p) (not b-proper-p)))
+             `(one-list-proper-one-improper ,a ,b)
+           (if a-proper-p
+               (if (not (equal (length a) (length b)))
+                   `(proper-lists-of-different-length ,(length a) ,(length b)
+                                                      ,a ,b
+                                                      first-mismatch-at
+                                                      ,(ert--mismatch a b))
+                 (loop for i from 0
+                       for ai in a
+                       for bi in b
+                       for xi = (ert--explain-not-equal ai bi)
+                       do (when xi (return `(list-elt ,i ,xi)))
+                       finally (assert (equal a b) t)))
+             (let ((car-x (ert--explain-not-equal (car a) (car b))))
+               (if car-x
+                   `(car ,car-x)
+                 (let ((cdr-x (ert--explain-not-equal (cdr a) (cdr b))))
+                   (if cdr-x
+                       `(cdr ,cdr-x)
+                     (assert (equal a b) t)
+                     nil))))))))
+      (array (if (not (equal (length a) (length b)))
+                 `(arrays-of-different-length ,(length a) ,(length b)
+                                              ,a ,b
+                                              ,@(unless (char-table-p a)
+                                                  `(first-mismatch-at
+                                                    ,(ert--mismatch a b))))
+               (loop for i from 0
+                     for ai across a
+                     for bi across b
+                     for xi = (ert--explain-not-equal ai bi)
+                     do (when xi (return `(array-elt ,i ,xi)))
+                     finally (assert (equal a b) t))))
+      (atom (if (not (equal a b))
+                (if (and (symbolp a) (symbolp b) (string= a b))
+                    `(different-symbols-with-the-same-name ,a ,b)
+                  `(different-atoms ,(ert--explain-format-atom a)
+                                    ,(ert--explain-format-atom b)))
+              nil)))))
+(put 'equal 'ert-explainer 'ert--explain-not-equal)
+
+(defun ert--significant-plist-keys (plist)
+  "Return the keys of PLIST that have non-null values, in order."
+  (assert (zerop (mod (length plist) 2)) t)
+  (loop for (key value . rest) on plist by #'cddr
+        unless (or (null value) (memq key accu)) collect key into accu
+        finally (return accu)))
+
+(defun ert--plist-difference-explanation (a b)
+  "Return a programmer-readable explanation of why A and B are different plists.
+
+Returns nil if they are equivalent, i.e., have the same value for
+each key, where absent values are treated as nil.  The order of
+key/value pairs in each list does not matter."
+  (assert (zerop (mod (length a) 2)) t)
+  (assert (zerop (mod (length b) 2)) t)
+  ;; Normalizing the plists would be another way to do this but it
+  ;; requires a total ordering on all lisp objects (since any object
+  ;; is valid as a text property key).  Perhaps defining such an
+  ;; ordering is useful in other contexts, too, but it's a lot of
+  ;; work, so let's punt on it for now.
+  (let* ((keys-a (ert--significant-plist-keys a))
+         (keys-b (ert--significant-plist-keys b))
+         (keys-in-a-not-in-b (ert--set-difference-eq keys-a keys-b))
+         (keys-in-b-not-in-a (ert--set-difference-eq keys-b keys-a)))
+    (flet ((explain-with-key (key)
+             (let ((value-a (plist-get a key))
+                   (value-b (plist-get b key)))
+               (assert (not (equal value-a value-b)) t)
+               `(different-properties-for-key
+                 ,key ,(ert--explain-not-equal-including-properties value-a
+                                                                    value-b)))))
+      (cond (keys-in-a-not-in-b
+             (explain-with-key (first keys-in-a-not-in-b)))
+            (keys-in-b-not-in-a
+             (explain-with-key (first keys-in-b-not-in-a)))
+            (t
+             (loop for key in keys-a
+                   when (not (equal (plist-get a key) (plist-get b key)))
+                   return (explain-with-key key)))))))
+
+(defun ert--abbreviate-string (s len suffixp)
+  "Shorten string S to at most LEN chars.
+
+If SUFFIXP is non-nil, returns a suffix of S, otherwise a prefix."
+  (let ((n (length s)))
+    (cond ((< n len)
+           s)
+          (suffixp
+           (substring s (- n len)))
+          (t
+           (substring s 0 len)))))
+
+(defun ert--explain-not-equal-including-properties (a b)
+  "Explainer function for `ert-equal-including-properties'.
+
+Returns a programmer-readable explanation of why A and B are not
+`ert-equal-including-properties', or nil if they are."
+  (if (not (equal a b))
+      (ert--explain-not-equal a b)
+    (assert (stringp a) t)
+    (assert (stringp b) t)
+    (assert (eql (length a) (length b)) t)
+    (loop for i from 0 to (length a)
+          for props-a = (text-properties-at i a)
+          for props-b = (text-properties-at i b)
+          for difference = (ert--plist-difference-explanation props-a props-b)
+          do (when difference
+               (return `(char ,i ,(substring-no-properties a i (1+ i))
+                              ,difference
+                              context-before
+                              ,(ert--abbreviate-string
+                                (substring-no-properties a 0 i)
+                                10 t)
+                              context-after
+                              ,(ert--abbreviate-string
+                                (substring-no-properties a (1+ i))
+                                10 nil))))
+          ;; TODO(ohler): Get `equal-including-properties' fixed in
+          ;; Emacs, delete `ert-equal-including-properties', and
+          ;; re-enable this assertion.
+          ;;finally (assert (equal-including-properties a b) t)
+          )))
+(put 'ert-equal-including-properties
+     'ert-explainer
+     'ert--explain-not-equal-including-properties)
+
+
+;;; Implementation of `ert-info'.
+
+;; TODO(ohler): The name `info' clashes with
+;; `ert--test-execution-info'.  One or both should be renamed.
+(defvar ert--infos '()
+  "The stack of `ert-info' infos that currently apply.
+
+Bound dynamically.  This is a list of (PREFIX . MESSAGE) pairs.")
+
+(defmacro* ert-info ((message-form &key ((:prefix prefix-form) "Info: "))
+                     &body body)
+  "Evaluate MESSAGE-FORM and BODY, and report the message if BODY fails.
+
+To be used within ERT tests.  MESSAGE-FORM should evaluate to a
+string that will be displayed together with the test result if
+the test fails.  PREFIX-FORM should evaluate to a string as well
+and is displayed in front of the value of MESSAGE-FORM."
+  (declare (debug ((form &rest [sexp form]) body))
+	   (indent 1))
+  `(let ((ert--infos (cons (cons ,prefix-form ,message-form) ert--infos)))
+     ,@body))
+
+
+
+;;; Facilities for running a single test.
+
+(defvar ert-debug-on-error nil
+  "Non-nil means enter debugger when a test fails or terminates with an error.")
+
+;; The data structures that represent the result of running a test.
+(defstruct ert-test-result
+  (messages nil)
+  (should-forms nil)
+  )
+(defstruct (ert-test-passed (:include ert-test-result)))
+(defstruct (ert-test-result-with-condition (:include ert-test-result))
+  (condition (assert nil))
+  (backtrace (assert nil))
+  (infos (assert nil)))
+(defstruct (ert-test-quit (:include ert-test-result-with-condition)))
+(defstruct (ert-test-failed (:include ert-test-result-with-condition)))
+(defstruct (ert-test-aborted-with-non-local-exit (:include ert-test-result)))
+
+
+(defun ert--record-backtrace ()
+  "Record the current backtrace (as a list) and return it."
+  ;; Since the backtrace is stored in the result object, result
+  ;; objects must only be printed with appropriate limits
+  ;; (`print-level' and `print-length') in place.  For interactive
+  ;; use, the cost of ensuring this possibly outweighs the advantage
+  ;; of storing the backtrace for
+  ;; `ert-results-pop-to-backtrace-for-test-at-point' given that we
+  ;; already have `ert-results-rerun-test-debugging-errors-at-point'.
+  ;; For batch use, however, printing the backtrace may be useful.
+  (loop
+   ;; 6 is the number of frames our own debugger adds (when
+   ;; compiled; more when interpreted).  FIXME: Need to describe a
+   ;; procedure for determining this constant.
+   for i from 6
+   for frame = (backtrace-frame i)
+   while frame
+   collect frame))
+
+(defun ert--print-backtrace (backtrace)
+  "Format the backtrace BACKTRACE to the current buffer."
+  ;; This is essentially a reimplementation of Fbacktrace
+  ;; (src/eval.c), but for a saved backtrace, not the current one.
+  (let ((print-escape-newlines t)
+        (print-level 8)
+        (print-length 50))
+    (dolist (frame backtrace)
+      (ecase (first frame)
+        ((nil)
+         ;; Special operator.
+         (destructuring-bind (special-operator &rest arg-forms)
+             (cdr frame)
+           (insert
+            (format "  %S\n" (list* special-operator arg-forms)))))
+        ((t)
+         ;; Function call.
+         (destructuring-bind (fn &rest args) (cdr frame)
+           (insert (format "  %S(" fn))
+           (loop for firstp = t then nil
+                 for arg in args do
+                 (unless firstp
+                   (insert " "))
+                 (insert (format "%S" arg)))
+           (insert ")\n")))))))
+
+;; A container for the state of the execution of a single test and
+;; environment data needed during its execution.
+(defstruct ert--test-execution-info
+  (test (assert nil))
+  (result (assert nil))
+  ;; A thunk that may be called when RESULT has been set to its final
+  ;; value and test execution should be terminated.  Should not
+  ;; return.
+  (exit-continuation (assert nil))
+  ;; The binding of `debugger' outside of the execution of the test.
+  next-debugger
+  ;; The binding of `ert-debug-on-error' that is in effect for the
+  ;; execution of the current test.  We store it to avoid being
+  ;; affected by any new bindings the test itself may establish.  (I
+  ;; don't remember whether this feature is important.)
+  ert-debug-on-error)
+
+(defun ert--run-test-debugger (info debugger-args)
+  "During a test run, `debugger' is bound to a closure that calls this function.
+
+This function records failures and errors and either terminates
+the test silently or calls the interactive debugger, as
+appropriate.
+
+INFO is the ert--test-execution-info corresponding to this test
+run.  DEBUGGER-ARGS are the arguments to `debugger'."
+  (destructuring-bind (first-debugger-arg &rest more-debugger-args)
+      debugger-args
+    (ecase first-debugger-arg
+      ((lambda debug t exit nil)
+       (apply (ert--test-execution-info-next-debugger info) debugger-args))
+      (error
+       (let* ((condition (first more-debugger-args))
+              (type (case (car condition)
+                      ((quit) 'quit)
+                      (otherwise 'failed)))
+              (backtrace (ert--record-backtrace))
+              (infos (reverse ert--infos)))
+         (setf (ert--test-execution-info-result info)
+               (ecase type
+                 (quit
+                  (make-ert-test-quit :condition condition
+                                      :backtrace backtrace
+                                      :infos infos))
+                 (failed
+                  (make-ert-test-failed :condition condition
+                                        :backtrace backtrace
+                                        :infos infos))))
+         ;; Work around Emacs' heuristic (in eval.c) for detecting
+         ;; errors in the debugger.
+         (incf num-nonmacro-input-events)
+         ;; FIXME: We should probably implement more fine-grained
+         ;; control a la non-t `debug-on-error' here.
+         (cond
+          ((ert--test-execution-info-ert-debug-on-error info)
+           (apply (ert--test-execution-info-next-debugger info) debugger-args))
+          (t))
+         (funcall (ert--test-execution-info-exit-continuation info)))))))
+
+(defun ert--run-test-internal (ert-test-execution-info)
+  "Low-level function to run a test according to ERT-TEST-EXECUTION-INFO.
+
+This mainly sets up debugger-related bindings."
+  (lexical-let ((info ert-test-execution-info))
+    (setf (ert--test-execution-info-next-debugger info) debugger
+          (ert--test-execution-info-ert-debug-on-error info) ert-debug-on-error)
+    (catch 'ert--pass
+      ;; For now, each test gets its own temp buffer and its own
+      ;; window excursion, just to be safe.  If this turns out to be
+      ;; too expensive, we can remove it.
+      (with-temp-buffer
+        (save-window-excursion
+          (let ((debugger (lambda (&rest debugger-args)
+                            (ert--run-test-debugger info debugger-args)))
+                (debug-on-error t)
+                (debug-on-quit t)
+                ;; FIXME: Do we need to store the old binding of this
+                ;; and consider it in `ert--run-test-debugger'?
+                (debug-ignored-errors nil)
+                (ert--infos '()))
+            (funcall (ert-test-body (ert--test-execution-info-test info))))))
+      (ert-pass))
+    (setf (ert--test-execution-info-result info) (make-ert-test-passed)))
+  nil)
+
+(defun ert--force-message-log-buffer-truncation ()
+  "Immediately truncate *Messages* buffer according to `message-log-max'.
+
+This can be useful after reducing the value of `message-log-max'."
+  (with-current-buffer (get-buffer-create "*Messages*")
+    ;; This is a reimplementation of this part of message_dolog() in xdisp.c:
+    ;; if (NATNUMP (Vmessage_log_max))
+    ;;   {
+    ;;     scan_newline (Z, Z_BYTE, BEG, BEG_BYTE,
+    ;;                   -XFASTINT (Vmessage_log_max) - 1, 0);
+    ;;     del_range_both (BEG, BEG_BYTE, PT, PT_BYTE, 0);
+    ;;   }
+    (when (and (integerp message-log-max) (>= message-log-max 0))
+      (let ((begin (point-min))
+            (end (save-excursion
+                   (goto-char (point-max))
+                   (forward-line (- message-log-max))
+                   (point))))
+        (delete-region begin end)))))
+
+(defvar ert--running-tests nil
+  "List of tests that are currently in execution.
+
+This list is empty while no test is running, has one element
+while a test is running, two elements while a test run from
+inside a test is running, etc.  The list is in order of nesting,
+innermost test first.
+
+The elements are of type `ert-test'.")
+
+(defun ert-run-test (ert-test)
+  "Run ERT-TEST.
+
+Returns the result and stores it in ERT-TEST's `most-recent-result' slot."
+  (setf (ert-test-most-recent-result ert-test) nil)
+  (block error
+    (lexical-let ((begin-marker
+                   (with-current-buffer (get-buffer-create "*Messages*")
+                     (set-marker (make-marker) (point-max)))))
+      (unwind-protect
+          (lexical-let ((info (make-ert--test-execution-info
+                               :test ert-test
+                               :result
+                               (make-ert-test-aborted-with-non-local-exit)
+                               :exit-continuation (lambda ()
+                                                    (return-from error nil))))
+                        (should-form-accu (list)))
+            (unwind-protect
+                (let ((ert--should-execution-observer
+                       (lambda (form-description)
+                         (push form-description should-form-accu)))
+                      (message-log-max t)
+                      (ert--running-tests (cons ert-test ert--running-tests)))
+                  (ert--run-test-internal info))
+              (let ((result (ert--test-execution-info-result info)))
+                (setf (ert-test-result-messages result)
+                      (with-current-buffer (get-buffer-create "*Messages*")
+                        (buffer-substring begin-marker (point-max))))
+                (ert--force-message-log-buffer-truncation)
+                (setq should-form-accu (nreverse should-form-accu))
+                (setf (ert-test-result-should-forms result)
+                      should-form-accu)
+                (setf (ert-test-most-recent-result ert-test) result))))
+        (set-marker begin-marker nil))))
+  (ert-test-most-recent-result ert-test))
+
+(defun ert-running-test ()
+  "Return the top-level test currently executing."
+  (car (last ert--running-tests)))
+
+
+;;; Test selectors.
+
+(defun ert-test-result-type-p (result result-type)
+  "Return non-nil if RESULT matches type RESULT-TYPE.
+
+Valid result types:
+
+nil -- Never matches.
+t -- Always matches.
+:failed, :passed -- Matches corresponding results.
+\(and TYPES...\) -- Matches if all TYPES match.
+\(or TYPES...\) -- Matches if some TYPES match.
+\(not TYPE\) -- Matches if TYPE does not match.
+\(satisfies PREDICATE\) -- Matches if PREDICATE returns true when called with
+                           RESULT."
+  ;; It would be easy to add `member' and `eql' types etc., but I
+  ;; haven't bothered yet.
+  (etypecase result-type
+    ((member nil) nil)
+    ((member t) t)
+    ((member :failed) (ert-test-failed-p result))
+    ((member :passed) (ert-test-passed-p result))
+    (cons
+     (destructuring-bind (operator &rest operands) result-type
+       (ecase operator
+         (and
+          (case (length operands)
+            (0 t)
+            (t
+             (and (ert-test-result-type-p result (first operands))
+                  (ert-test-result-type-p result `(and ,@(rest operands)))))))
+         (or
+          (case (length operands)
+            (0 nil)
+            (t
+             (or (ert-test-result-type-p result (first operands))
+                 (ert-test-result-type-p result `(or ,@(rest operands)))))))
+         (not
+          (assert (eql (length operands) 1))
+          (not (ert-test-result-type-p result (first operands))))
+         (satisfies
+          (assert (eql (length operands) 1))
+          (funcall (first operands) result)))))))
+
+(defun ert-test-result-expected-p (test result)
+  "Return non-nil if TEST's expected result type matches RESULT."
+  (ert-test-result-type-p result (ert-test-expected-result-type test)))
+
+(defun ert-select-tests (selector universe)
+  "Return the tests that match SELECTOR.
+
+UNIVERSE specifies the set of tests to select from; it should be
+a list of tests, or t, which refers to all tests named by symbols
+in `obarray'.
+
+Returns the set of tests as a list.
+
+Valid selectors:
+
+nil -- Selects the empty set.
+t -- Selects UNIVERSE.
+:new -- Selects all tests that have not been run yet.
+:failed, :passed -- Select tests according to their most recent result.
+:expected, :unexpected -- Select tests according to their most recent result.
+a string -- Selects all tests that have a name that matches the string,
+            a regexp.
+a test -- Selects that test.
+a symbol -- Selects the test that the symbol names, errors if none.
+\(member TESTS...\) -- Selects TESTS, a list of tests or symbols naming tests.
+\(eql TEST\) -- Selects TEST, a test or a symbol naming a test.
+\(and SELECTORS...\) -- Selects the tests that match all SELECTORS.
+\(or SELECTORS...\) -- Selects the tests that match any SELECTOR.
+\(not SELECTOR\) -- Selects all tests that do not match SELECTOR.
+\(tag TAG) -- Selects all tests that have TAG on their tags list.
+\(satisfies PREDICATE\) -- Selects all tests that satisfy PREDICATE.
+
+Only selectors that require a superset of tests, such
+as (satisfies ...), strings, :new, etc. make use of UNIVERSE.
+Selectors that do not, such as \(member ...\), just return the
+set implied by them without checking whether it is really
+contained in UNIVERSE."
+  ;; This code needs to match the etypecase in
+  ;; `ert-insert-human-readable-selector'.
+  (etypecase selector
+    ((member nil) nil)
+    ((member t) (etypecase universe
+                  (list universe)
+                  ((member t) (ert-select-tests "" universe))))
+    ((member :new) (ert-select-tests
+                    `(satisfies ,(lambda (test)
+                                   (null (ert-test-most-recent-result test))))
+                    universe))
+    ((member :failed) (ert-select-tests
+                       `(satisfies ,(lambda (test)
+                                      (ert-test-result-type-p
+                                       (ert-test-most-recent-result test)
+                                       ':failed)))
+                       universe))
+    ((member :passed) (ert-select-tests
+                       `(satisfies ,(lambda (test)
+                                      (ert-test-result-type-p
+                                       (ert-test-most-recent-result test)
+                                       ':passed)))
+                       universe))
+    ((member :expected) (ert-select-tests
+                         `(satisfies
+                           ,(lambda (test)
+                              (ert-test-result-expected-p
+                               test
+                               (ert-test-most-recent-result test))))
+                         universe))
+    ((member :unexpected) (ert-select-tests `(not :expected) universe))
+    (string
+     (etypecase universe
+       ((member t) (mapcar #'ert-get-test
+                           (apropos-internal selector #'ert-test-boundp)))
+       (list (ert--remove-if-not (lambda (test)
+                                   (and (ert-test-name test)
+                                        (string-match selector
+                                                      (ert-test-name test))))
+                                 universe))))
+    (ert-test (list selector))
+    (symbol
+     (assert (ert-test-boundp selector))
+     (list (ert-get-test selector)))
+    (cons
+     (destructuring-bind (operator &rest operands) selector
+       (ecase operator
+         (member
+          (mapcar (lambda (purported-test)
+                    (etypecase purported-test
+                      (symbol (assert (ert-test-boundp purported-test))
+                              (ert-get-test purported-test))
+                      (ert-test purported-test)))
+                  operands))
+         (eql
+          (assert (eql (length operands) 1))
+          (ert-select-tests `(member ,@operands) universe))
+         (and
+          ;; Do these definitions of AND, NOT and OR satisfy de
+          ;; Morgan's laws?  Should they?
+          (case (length operands)
+            (0 (ert-select-tests 't universe))
+            (t (ert-select-tests `(and ,@(rest operands))
+                                 (ert-select-tests (first operands)
+                                                   universe)))))
+         (not
+          (assert (eql (length operands) 1))
+          (let ((all-tests (ert-select-tests 't universe)))
+            (ert--set-difference all-tests
+                                 (ert-select-tests (first operands)
+                                                   all-tests))))
+         (or
+          (case (length operands)
+            (0 (ert-select-tests 'nil universe))
+            (t (ert--union (ert-select-tests (first operands) universe)
+                           (ert-select-tests `(or ,@(rest operands))
+                                             universe)))))
+         (tag
+          (assert (eql (length operands) 1))
+          (let ((tag (first operands)))
+            (ert-select-tests `(satisfies
+                                ,(lambda (test)
+                                   (member tag (ert-test-tags test))))
+                              universe)))
+         (satisfies
+          (assert (eql (length operands) 1))
+          (ert--remove-if-not (first operands)
+                              (ert-select-tests 't universe))))))))
+
+(defun ert--insert-human-readable-selector (selector)
+  "Insert a human-readable presentation of SELECTOR into the current buffer."
+  ;; This is needed to avoid printing the (huge) contents of the
+  ;; `backtrace' slot of the result objects in the
+  ;; `most-recent-result' slots of test case objects in (eql ...) or
+  ;; (member ...) selectors.
+  (labels ((rec (selector)
+             ;; This code needs to match the etypecase in `ert-select-tests'.
+             (etypecase selector
+               ((or (member nil t
+                            :new :failed :passed
+                            :expected :unexpected)
+                    string
+                    symbol)
+                selector)
+               (ert-test
+                (if (ert-test-name selector)
+                    (make-symbol (format "<%S>" (ert-test-name selector)))
+                  (make-symbol "<unnamed test>")))
+               (cons
+                (destructuring-bind (operator &rest operands) selector
+                  (ecase operator
+                    ((member eql and not or)
+                     `(,operator ,@(mapcar #'rec operands)))
+                    ((member tag satisfies)
+                     selector)))))))
+    (insert (format "%S" (rec selector)))))
+
+
+;;; Facilities for running a whole set of tests.
+
+;; The data structure that contains the set of tests being executed
+;; during one particular test run, their results, the state of the
+;; execution, and some statistics.
+;;
+;; The data about results and expected results of tests may seem
+;; redundant here, since the test objects also carry such information.
+;; However, the information in the test objects may be more recent, it
+;; may correspond to a different test run.  We need the information
+;; that corresponds to this run in order to be able to update the
+;; statistics correctly when a test is re-run interactively and has a
+;; different result than before.
+(defstruct ert--stats
+  (selector (assert nil))
+  ;; The tests, in order.
+  (tests (assert nil) :type vector)
+  ;; A map of test names (or the test objects themselves for unnamed
+  ;; tests) to indices into the `tests' vector.
+  (test-map (assert nil) :type hash-table)
+  ;; The results of the tests during this run, in order.
+  (test-results (assert nil) :type vector)
+  ;; The start times of the tests, in order, as reported by
+  ;; `current-time'.
+  (test-start-times (assert nil) :type vector)
+  ;; The end times of the tests, in order, as reported by
+  ;; `current-time'.
+  (test-end-times (assert nil) :type vector)
+  (passed-expected 0)
+  (passed-unexpected 0)
+  (failed-expected 0)
+  (failed-unexpected 0)
+  (start-time nil)
+  (end-time nil)
+  (aborted-p nil)
+  (current-test nil)
+  ;; The time at or after which the next redisplay should occur, as a
+  ;; float.
+  (next-redisplay 0.0))
+
+(defun ert-stats-completed-expected (stats)
+  "Return the number of tests in STATS that had expected results."
+  (+ (ert--stats-passed-expected stats)
+     (ert--stats-failed-expected stats)))
+
+(defun ert-stats-completed-unexpected (stats)
+  "Return the number of tests in STATS that had unexpected results."
+  (+ (ert--stats-passed-unexpected stats)
+     (ert--stats-failed-unexpected stats)))
+
+(defun ert-stats-completed (stats)
+  "Number of tests in STATS that have run so far."
+  (+ (ert-stats-completed-expected stats)
+     (ert-stats-completed-unexpected stats)))
+
+(defun ert-stats-total (stats)
+  "Number of tests in STATS, regardless of whether they have run yet."
+  (length (ert--stats-tests stats)))
+
+;; The stats object of the current run, dynamically bound.  This is
+;; used for the mode line progress indicator.
+(defvar ert--current-run-stats nil)
+
+(defun ert--stats-test-key (test)
+  "Return the key used for TEST in the test map of ert--stats objects.
+
+Returns the name of TEST if it has one, or TEST itself otherwise."
+  (or (ert-test-name test) test))
+
+(defun ert--stats-set-test-and-result (stats pos test result)
+  "Change STATS by replacing the test at position POS with TEST and RESULT.
+
+Also changes the counters in STATS to match."
+  (let* ((tests (ert--stats-tests stats))
+         (results (ert--stats-test-results stats))
+         (old-test (aref tests pos))
+         (map (ert--stats-test-map stats)))
+    (flet ((update (d)
+             (if (ert-test-result-expected-p (aref tests pos)
+                                             (aref results pos))
+                 (etypecase (aref results pos)
+                   (ert-test-passed (incf (ert--stats-passed-expected stats) d))
+                   (ert-test-failed (incf (ert--stats-failed-expected stats) d))
+                   (null)
+                   (ert-test-aborted-with-non-local-exit))
+               (etypecase (aref results pos)
+                 (ert-test-passed (incf (ert--stats-passed-unexpected stats) d))
+                 (ert-test-failed (incf (ert--stats-failed-unexpected stats) d))
+                 (null)
+                 (ert-test-aborted-with-non-local-exit)))))
+      ;; Adjust counters to remove the result that is currently in stats.
+      (update -1)
+      ;; Put new test and result into stats.
+      (setf (aref tests pos) test
+            (aref results pos) result)
+      (remhash (ert--stats-test-key old-test) map)
+      (setf (gethash (ert--stats-test-key test) map) pos)
+      ;; Adjust counters to match new result.
+      (update +1)
+      nil)))
+
+(defun ert--make-stats (tests selector)
+  "Create a new `ert--stats' object for running TESTS.
+
+SELECTOR is the selector that was used to select TESTS."
+  (setq tests (ert--coerce-to-vector tests))
+  (let ((map (make-hash-table :size (length tests))))
+    (loop for i from 0
+          for test across tests
+          for key = (ert--stats-test-key test) do
+          (assert (not (gethash key map)))
+          (setf (gethash key map) i))
+    (make-ert--stats :selector selector
+                     :tests tests
+                     :test-map map
+                     :test-results (make-vector (length tests) nil)
+                     :test-start-times (make-vector (length tests) nil)
+                     :test-end-times (make-vector (length tests) nil))))
+
+(defun ert-run-or-rerun-test (stats test listener)
+  ;; checkdoc-order: nil
+  "Run the single test TEST and record the result using STATS and LISTENER."
+  (let ((ert--current-run-stats stats)
+        (pos (ert--stats-test-pos stats test)))
+    (ert--stats-set-test-and-result stats pos test nil)
+    ;; Call listener after setting/before resetting
+    ;; (ert--stats-current-test stats); the listener might refresh the
+    ;; mode line display, and if the value is not set yet/any more
+    ;; during this refresh, the mode line will flicker unnecessarily.
+    (setf (ert--stats-current-test stats) test)
+    (funcall listener 'test-started stats test)
+    (setf (ert-test-most-recent-result test) nil)
+    (setf (aref (ert--stats-test-start-times stats) pos) (current-time))
+    (unwind-protect
+        (ert-run-test test)
+      (setf (aref (ert--stats-test-end-times stats) pos) (current-time))
+      (let ((result (ert-test-most-recent-result test)))
+        (ert--stats-set-test-and-result stats pos test result)
+        (funcall listener 'test-ended stats test result))
+      (setf (ert--stats-current-test stats) nil))))
+
+(defun ert-run-tests (selector listener)
+  "Run the tests specified by SELECTOR, sending progress updates to LISTENER."
+  (let* ((tests (ert-select-tests selector t))
+         (stats (ert--make-stats tests selector)))
+    (setf (ert--stats-start-time stats) (current-time))
+    (funcall listener 'run-started stats)
+    (let ((abortedp t))
+      (unwind-protect
+          (let ((ert--current-run-stats stats))
+            (force-mode-line-update)
+            (unwind-protect
+                (progn
+                  (loop for test in tests do
+                        (ert-run-or-rerun-test stats test listener))
+                  (setq abortedp nil))
+              (setf (ert--stats-aborted-p stats) abortedp)
+              (setf (ert--stats-end-time stats) (current-time))
+              (funcall listener 'run-ended stats abortedp)))
+        (force-mode-line-update))
+      stats)))
+
+(defun ert--stats-test-pos (stats test)
+  ;; checkdoc-order: nil
+  "Return the position (index) of TEST in the run represented by STATS."
+  (gethash (ert--stats-test-key test) (ert--stats-test-map stats)))
+
+
+;;; Formatting functions shared across UIs.
+
+(defun ert--format-time-iso8601 (time)
+  "Format TIME in the variant of ISO 8601 used for timestamps in ERT."
+  (format-time-string "%Y-%m-%d %T%z" time))
+
+(defun ert-char-for-test-result (result expectedp)
+  "Return a character that represents the test result RESULT.
+
+EXPECTEDP specifies whether the result was expected."
+  (let ((s (etypecase result
+             (ert-test-passed ".P")
+             (ert-test-failed "fF")
+             (null "--")
+             (ert-test-aborted-with-non-local-exit "aA"))))
+    (elt s (if expectedp 0 1))))
+
+(defun ert-string-for-test-result (result expectedp)
+  "Return a string that represents the test result RESULT.
+
+EXPECTEDP specifies whether the result was expected."
+  (let ((s (etypecase result
+             (ert-test-passed '("passed" "PASSED"))
+             (ert-test-failed '("failed" "FAILED"))
+             (null '("unknown" "UNKNOWN"))
+             (ert-test-aborted-with-non-local-exit '("aborted" "ABORTED")))))
+    (elt s (if expectedp 0 1))))
+
+(defun ert--pp-with-indentation-and-newline (object)
+  "Pretty-print OBJECT, indenting it to the current column of point.
+Ensures a final newline is inserted."
+  (let ((begin (point)))
+    (pp object (current-buffer))
+    (unless (bolp) (insert "\n"))
+    (save-excursion
+      (goto-char begin)
+      (indent-sexp))))
+
+(defun ert--insert-infos (result)
+  "Insert `ert-info' infos from RESULT into current buffer.
+
+RESULT must be an `ert-test-result-with-condition'."
+  (check-type result ert-test-result-with-condition)
+  (dolist (info (ert-test-result-with-condition-infos result))
+    (destructuring-bind (prefix . message) info
+      (let ((begin (point))
+            (indentation (make-string (+ (length prefix) 4) ?\s))
+            (end nil))
+        (unwind-protect
+            (progn
+              (insert message "\n")
+              (setq end (copy-marker (point)))
+              (goto-char begin)
+              (insert "    " prefix)
+              (forward-line 1)
+              (while (< (point) end)
+                (insert indentation)
+                (forward-line 1)))
+          (when end (set-marker end nil)))))))
+
+
+;;; Running tests in batch mode.
+
+(defvar ert-batch-backtrace-right-margin 70
+  "*The maximum line length for printing backtraces in `ert-run-tests-batch'.")
+
+;;;###autoload
+(defun ert-run-tests-batch (&optional selector)
+  "Run the tests specified by SELECTOR, printing results to the terminal.
+
+SELECTOR works as described in `ert-select-tests', except if
+SELECTOR is nil, in which case all tests rather than none will be
+run; this makes the command line \"emacs -batch -l my-tests.el -f
+ert-run-tests-batch-and-exit\" useful.
+
+Returns the stats object."
+  (unless selector (setq selector 't))
+  (ert-run-tests
+   selector
+   (lambda (event-type &rest event-args)
+     (ecase event-type
+       (run-started
+        (destructuring-bind (stats) event-args
+          (message "Running %s tests (%s)"
+                   (length (ert--stats-tests stats))
+                   (ert--format-time-iso8601 (ert--stats-start-time stats)))))
+       (run-ended
+        (destructuring-bind (stats abortedp) event-args
+          (let ((unexpected (ert-stats-completed-unexpected stats))
+                (expected-failures (ert--stats-failed-expected stats)))
+            (message "\n%sRan %s tests, %s results as expected%s (%s)%s\n"
+                     (if (not abortedp)
+                         ""
+                       "Aborted: ")
+                     (ert-stats-total stats)
+                     (ert-stats-completed-expected stats)
+                     (if (zerop unexpected)
+                         ""
+                       (format ", %s unexpected" unexpected))
+                     (ert--format-time-iso8601 (ert--stats-end-time stats))
+                     (if (zerop expected-failures)
+                         ""
+                       (format "\n%s expected failures" expected-failures)))
+            (unless (zerop unexpected)
+              (message "%s unexpected results:" unexpected)
+              (loop for test across (ert--stats-tests stats)
+                    for result = (ert-test-most-recent-result test) do
+                    (when (not (ert-test-result-expected-p test result))
+                      (message "%9s  %S"
+                               (ert-string-for-test-result result nil)
+                               (ert-test-name test))))
+              (message "%s" "")))))
+       (test-started
+        )
+       (test-ended
+        (destructuring-bind (stats test result) event-args
+          (unless (ert-test-result-expected-p test result)
+            (etypecase result
+              (ert-test-passed
+               (message "Test %S passed unexpectedly" (ert-test-name test)))
+              (ert-test-result-with-condition
+               (message "Test %S backtrace:" (ert-test-name test))
+               (with-temp-buffer
+                 (ert--print-backtrace (ert-test-result-with-condition-backtrace
+                                        result))
+                 (goto-char (point-min))
+                 (while (not (eobp))
+                   (let ((start (point))
+                         (end (progn (end-of-line) (point))))
+                     (setq end (min end
+                                    (+ start ert-batch-backtrace-right-margin)))
+                     (message "%s" (buffer-substring-no-properties
+                                    start end)))
+                   (forward-line 1)))
+               (with-temp-buffer
+                 (ert--insert-infos result)
+                 (insert "    ")
+                 (let ((print-escape-newlines t)
+                       (print-level 5)
+                       (print-length 10))
+                   (let ((begin (point)))
+                     (ert--pp-with-indentation-and-newline
+                      (ert-test-result-with-condition-condition result))))
+                 (goto-char (1- (point-max)))
+                 (assert (looking-at "\n"))
+                 (delete-char 1)
+                 (message "Test %S condition:" (ert-test-name test))
+                 (message "%s" (buffer-string))))
+              (ert-test-aborted-with-non-local-exit
+               (message "Test %S aborted with non-local exit"
+                        (ert-test-name test)))))
+          (let* ((max (prin1-to-string (length (ert--stats-tests stats))))
+                 (format-string (concat "%9s  %"
+                                        (prin1-to-string (length max))
+                                        "s/" max "  %S")))
+            (message format-string
+                     (ert-string-for-test-result result
+                                                 (ert-test-result-expected-p
+                                                  test result))
+                     (1+ (ert--stats-test-pos stats test))
+                     (ert-test-name test)))))))))
+
+;;;###autoload
+(defun ert-run-tests-batch-and-exit (&optional selector)
+  "Like `ert-run-tests-batch', but exits Emacs when done.
+
+The exit status will be 0 if all test results were as expected, 1
+on unexpected results, or 2 if the tool detected an error outside
+of the tests (e.g. invalid SELECTOR or bug in the code that runs
+the tests)."
+  (unwind-protect
+      (let ((stats (ert-run-tests-batch selector)))
+        (kill-emacs (if (zerop (ert-stats-completed-unexpected stats)) 0 1)))
+    (unwind-protect
+        (progn
+          (message "Error running tests")
+          (backtrace))
+      (kill-emacs 2))))
+
+
+;;; Utility functions for load/unload actions.
+
+(defun ert--activate-font-lock-keywords ()
+  "Activate font-lock keywords for some of ERT's symbols."
+  (font-lock-add-keywords
+   nil
+   '(("(\\(\\<ert-deftest\\)\\>\\s *\\(\\sw+\\)?"
+      (1 font-lock-keyword-face nil t)
+      (2 font-lock-function-name-face nil t)))))
+
+(defun* ert--remove-from-list (list-var element &key key test)
+  "Remove ELEMENT from the value of LIST-VAR if present.
+
+This can be used as an inverse of `add-to-list'."
+  (unless key (setq key #'identity))
+  (unless test (setq test #'equal))
+  (setf (symbol-value list-var)
+        (ert--remove* element
+                      (symbol-value list-var)
+                      :key key
+                      :test test)))
+
+
+;;; Some basic interactive functions.
+
+(defun ert-read-test-name (prompt &optional default history
+                                  add-default-to-prompt)
+  "Read the name of a test and return it as a symbol.
+
+Prompt with PROMPT.  If DEFAULT is a valid test name, use it as a
+default.  HISTORY is the history to use; see `completing-read'.
+If ADD-DEFAULT-TO-PROMPT is non-nil, PROMPT will be modified to
+include the default, if any.
+
+Signals an error if no test name was read."
+  (etypecase default
+    (string (let ((symbol (intern-soft default)))
+              (unless (and symbol (ert-test-boundp symbol))
+                (setq default nil))))
+    (symbol (setq default
+                  (if (ert-test-boundp default)
+                      (symbol-name default)
+                    nil)))
+    (ert-test (setq default (ert-test-name default))))
+  (when add-default-to-prompt
+    (setq prompt (if (null default)
+                     (format "%s: " prompt)
+                   (format "%s (default %s): " prompt default))))
+  (let ((input (completing-read prompt obarray #'ert-test-boundp
+                                t nil history default nil)))
+    ;; completing-read returns an empty string if default was nil and
+    ;; the user just hit enter.
+    (let ((sym (intern-soft input)))
+      (if (ert-test-boundp sym)
+          sym
+        (error "Input does not name a test")))))
+
+(defun ert-read-test-name-at-point (prompt)
+  "Read the name of a test and return it as a symbol.
+As a default, use the symbol at point, or the test at point if in
+the ERT results buffer.  Prompt with PROMPT, augmented with the
+default (if any)."
+  (ert-read-test-name prompt (ert-test-at-point) nil t))
+
+(defun ert-find-test-other-window (test-name)
+  "Find, in another window, the definition of TEST-NAME."
+  (interactive (list (ert-read-test-name-at-point "Find test definition: ")))
+  (find-function-do-it test-name 'ert-deftest 'switch-to-buffer-other-window))
+
+(defun ert-delete-test (test-name)
+  "Make the test TEST-NAME unbound.
+
+Nothing more than an interactive interface to `ert-make-test-unbound'."
+  (interactive (list (ert-read-test-name-at-point "Delete test")))
+  (ert-make-test-unbound test-name))
+
+(defun ert-delete-all-tests ()
+  "Make all symbols in `obarray' name no test."
+  (interactive)
+  (when (interactive-p)
+    (unless (y-or-n-p "Delete all tests? ")
+      (error "Aborted")))
+  ;; We can't use `ert-select-tests' here since that gives us only
+  ;; test objects, and going from them back to the test name symbols
+  ;; can fail if the `ert-test' defstruct has been redefined.
+  (mapc #'ert-make-test-unbound (apropos-internal "" #'ert-test-boundp))
+  t)
+
+
+;;; Display of test progress and results.
+
+;; An entry in the results buffer ewoc.  There is one entry per test.
+(defstruct ert--ewoc-entry
+  (test (assert nil))
+  ;; If the result of this test was expected, its ewoc entry is hidden
+  ;; initially.
+  (hidden-p (assert nil))
+  ;; An ewoc entry may be collapsed to hide details such as the error
+  ;; condition.
+  ;;
+  ;; I'm not sure the ability to expand and collapse entries is still
+  ;; a useful feature.
+  (expanded-p t)
+  ;; By default, the ewoc entry presents the error condition with
+  ;; certain limits on how much to print (`print-level',
+  ;; `print-length').  The user can interactively switch to a set of
+  ;; higher limits.
+  (extended-printer-limits-p nil))
+
+;; Variables local to the results buffer.
+
+;; The ewoc.
+(defvar ert--results-ewoc)
+;; The stats object.
+(defvar ert--results-stats)
+;; A string with one character per test.  Each character represents
+;; the result of the corresponding test.  The string is displayed near
+;; the top of the buffer and serves as a progress bar.
+(defvar ert--results-progress-bar-string)
+;; The position where the progress bar button begins.
+(defvar ert--results-progress-bar-button-begin)
+;; The test result listener that updates the buffer when tests are run.
+(defvar ert--results-listener)
+
+(defun ert-insert-test-name-button (test-name)
+  "Insert a button that links to TEST-NAME."
+  (insert-text-button (format "%S" test-name)
+                      :type 'ert--test-name-button
+                      'ert-test-name test-name))
+
+(defun ert--results-format-expected-unexpected (expected unexpected)
+  "Return a string indicating EXPECTED expected results, UNEXPECTED unexpected."
+  (if (zerop unexpected)
+      (format "%s" expected)
+    (format "%s (%s unexpected)" (+ expected unexpected) unexpected)))
+
+(defun ert--results-update-ewoc-hf (ewoc stats)
+  "Update the header and footer of EWOC to show certain information from STATS.
+
+Also sets `ert--results-progress-bar-button-begin'."
+  (let ((run-count (ert-stats-completed stats))
+        (results-buffer (current-buffer))
+        ;; Need to save buffer-local value.
+        (font-lock font-lock-mode))
+    (ewoc-set-hf
+     ewoc
+     ;; header
+     (with-temp-buffer
+       (insert "Selector: ")
+       (ert--insert-human-readable-selector (ert--stats-selector stats))
+       (insert "\n")
+       (insert
+        (format (concat "Passed: %s\n"
+                        "Failed: %s\n"
+                        "Total:  %s/%s\n\n")
+                (ert--results-format-expected-unexpected
+                 (ert--stats-passed-expected stats)
+                 (ert--stats-passed-unexpected stats))
+                (ert--results-format-expected-unexpected
+                 (ert--stats-failed-expected stats)
+                 (ert--stats-failed-unexpected stats))
+                run-count
+                (ert-stats-total stats)))
+       (insert
+        (format "Started at:   %s\n"
+                (ert--format-time-iso8601 (ert--stats-start-time stats))))
+       ;; FIXME: This is ugly.  Need to properly define invariants of
+       ;; the `stats' data structure.
+       (let ((state (cond ((ert--stats-aborted-p stats) 'aborted)
+                          ((ert--stats-current-test stats) 'running)
+                          ((ert--stats-end-time stats) 'finished)
+                          (t 'preparing))))
+         (ecase state
+           (preparing
+            (insert ""))
+           (aborted
+            (cond ((ert--stats-current-test stats)
+                   (insert "Aborted during test: ")
+                   (ert-insert-test-name-button
+                    (ert-test-name (ert--stats-current-test stats))))
+                  (t
+                   (insert "Aborted."))))
+           (running
+            (assert (ert--stats-current-test stats))
+            (insert "Running test: ")
+            (ert-insert-test-name-button (ert-test-name
+                                          (ert--stats-current-test stats))))
+           (finished
+            (assert (not (ert--stats-current-test stats)))
+            (insert "Finished.")))
+         (insert "\n")
+         (if (ert--stats-end-time stats)
+             (insert
+              (format "%s%s\n"
+                      (if (ert--stats-aborted-p stats)
+                          "Aborted at:   "
+                        "Finished at:  ")
+                      (ert--format-time-iso8601 (ert--stats-end-time stats))))
+           (insert "\n"))
+         (insert "\n"))
+       (let ((progress-bar-string (with-current-buffer results-buffer
+                                    ert--results-progress-bar-string)))
+         (let ((progress-bar-button-begin
+                (insert-text-button progress-bar-string
+                                    :type 'ert--results-progress-bar-button
+                                    'face (or (and font-lock
+                                                   (ert-face-for-stats stats))
+                                              'button))))
+           ;; The header gets copied verbatim to the results buffer,
+           ;; and all positions remain the same, so
+           ;; `progress-bar-button-begin' will be the right position
+           ;; even in the results buffer.
+           (with-current-buffer results-buffer
+             (set (make-local-variable 'ert--results-progress-bar-button-begin)
+                  progress-bar-button-begin))))
+       (insert "\n\n")
+       (buffer-string))
+     ;; footer
+     ;;
+     ;; We actually want an empty footer, but that would trigger a bug
+     ;; in ewoc, sometimes clearing the entire buffer.  (It's possible
+     ;; that this bug has been fixed since this has been tested; we
+     ;; should test it again.)
+     "\n")))
+
+
+(defvar ert-test-run-redisplay-interval-secs .1
+  "How many seconds ERT should wait between redisplays while running tests.
+
+While running tests, ERT shows the current progress, and this variable
+determines how frequently the progress display is updated.")
+
+(defun ert--results-update-stats-display (ewoc stats)
+  "Update EWOC and the mode line to show data from STATS."
+  ;; TODO(ohler): investigate using `make-progress-reporter'.
+  (ert--results-update-ewoc-hf ewoc stats)
+  (force-mode-line-update)
+  (redisplay t)
+  (setf (ert--stats-next-redisplay stats)
+        (+ (float-time) ert-test-run-redisplay-interval-secs)))
+
+(defun ert--results-update-stats-display-maybe (ewoc stats)
+  "Call `ert--results-update-stats-display' if not called recently.
+
+EWOC and STATS are arguments for `ert--results-update-stats-display'."
+  (when (>= (float-time) (ert--stats-next-redisplay stats))
+    (ert--results-update-stats-display ewoc stats)))
+
+(defun ert--tests-running-mode-line-indicator ()
+  "Return a string for the mode line that shows the test run progress."
+  (let* ((stats ert--current-run-stats)
+         (tests-total (ert-stats-total stats))
+         (tests-completed (ert-stats-completed stats)))
+    (if (>= tests-completed tests-total)
+        (format " ERT(%s/%s,finished)" tests-completed tests-total)
+      (format " ERT(%s/%s):%s"
+              (1+ tests-completed)
+              tests-total
+              (if (null (ert--stats-current-test stats))
+                  "?"
+                (format "%S"
+                        (ert-test-name (ert--stats-current-test stats))))))))
+
+(defun ert--make-xrefs-region (begin end)
+  "Attach cross-references to function names between BEGIN and END.
+
+BEGIN and END specify a region in the current buffer."
+  (save-excursion
+    (save-restriction
+      (narrow-to-region begin (point))
+      ;; Inhibit optimization in `debugger-make-xrefs' that would
+      ;; sometimes insert unrelated backtrace info into our buffer.
+      (let ((debugger-previous-backtrace nil))
+        (debugger-make-xrefs)))))
+
+(defun ert--string-first-line (s)
+  "Return the first line of S, or S if it contains no newlines.
+
+The return value does not include the line terminator."
+  (substring s 0 (ert--string-position ?\n s)))
+
+(defun ert-face-for-test-result (expectedp)
+  "Return a face that shows whether a test result was expected or unexpected.
+
+If EXPECTEDP is nil, returns the face for unexpected results; if
+non-nil, returns the face for expected results.."
+  (if expectedp 'ert-test-result-expected 'ert-test-result-unexpected))
+
+(defun ert-face-for-stats (stats)
+  "Return a face that represents STATS."
+  (cond ((ert--stats-aborted-p stats) 'nil)
+        ((plusp (ert-stats-completed-unexpected stats))
+         (ert-face-for-test-result nil))
+        ((eql (ert-stats-completed-expected stats) (ert-stats-total stats))
+         (ert-face-for-test-result t))
+        (t 'nil)))
+
+(defun ert--print-test-for-ewoc (entry)
+  "The ewoc print function for ewoc test entries.  ENTRY is the entry to print."
+  (let* ((test (ert--ewoc-entry-test entry))
+         (stats ert--results-stats)
+         (result (let ((pos (ert--stats-test-pos stats test)))
+                   (assert pos)
+                   (aref (ert--stats-test-results stats) pos)))
+         (hiddenp (ert--ewoc-entry-hidden-p entry))
+         (expandedp (ert--ewoc-entry-expanded-p entry))
+         (extended-printer-limits-p (ert--ewoc-entry-extended-printer-limits-p
+                                     entry)))
+    (cond (hiddenp)
+          (t
+           (let ((expectedp (ert-test-result-expected-p test result)))
+             (insert-text-button (format "%c" (ert-char-for-test-result
+                                               result expectedp))
+                                 :type 'ert--results-expand-collapse-button
+                                 'face (or (and font-lock-mode
+                                                (ert-face-for-test-result
+                                                 expectedp))
+                                           'button)))
+           (insert " ")
+           (ert-insert-test-name-button (ert-test-name test))
+           (insert "\n")
+           (when (and expandedp (not (eql result 'nil)))
+             (when (ert-test-documentation test)
+               (insert "    "
+                       (propertize
+                        (ert--string-first-line (ert-test-documentation test))
+                        'font-lock-face 'font-lock-doc-face)
+                       "\n"))
+             (etypecase result
+               (ert-test-passed
+                (if (ert-test-result-expected-p test result)
+                    (insert "    passed\n")
+                  (insert "    passed unexpectedly\n"))
+                (insert ""))
+               (ert-test-result-with-condition
+                (ert--insert-infos result)
+                (let ((print-escape-newlines t)
+                      (print-level (if extended-printer-limits-p 12 6))
+                      (print-length (if extended-printer-limits-p 100 10)))
+                  (insert "    ")
+                  (let ((begin (point)))
+                    (ert--pp-with-indentation-and-newline
+                     (ert-test-result-with-condition-condition result))
+                    (ert--make-xrefs-region begin (point)))))
+               (ert-test-aborted-with-non-local-exit
+                (insert "    aborted\n")))
+             (insert "\n")))))
+  nil)
+
+(defun ert--results-font-lock-function (enabledp)
+  "Redraw the ERT results buffer after font-lock-mode was switched on or off.
+
+ENABLEDP is true if font-lock-mode is switched on, false
+otherwise."
+  (ert--results-update-ewoc-hf ert--results-ewoc ert--results-stats)
+  (ewoc-refresh ert--results-ewoc)
+  (font-lock-default-function enabledp))
+
+(defun ert--setup-results-buffer (stats listener buffer-name)
+  "Set up a test results buffer.
+
+STATS is the stats object; LISTENER is the results listener;
+BUFFER-NAME, if non-nil, is the buffer name to use."
+  (unless buffer-name (setq buffer-name "*ert*"))
+  (let ((buffer (get-buffer-create buffer-name)))
+    (with-current-buffer buffer
+      (setq buffer-read-only t)
+      (let ((inhibit-read-only t))
+        (buffer-disable-undo)
+        (erase-buffer)
+        (ert-results-mode)
+        ;; Erase buffer again in case switching out of the previous
+        ;; mode inserted anything.  (This happens e.g. when switching
+        ;; from ert-results-mode to ert-results-mode when
+        ;; font-lock-mode turns itself off in change-major-mode-hook.)
+        (erase-buffer)
+        (set (make-local-variable 'font-lock-function)
+             'ert--results-font-lock-function)
+        (let ((ewoc (ewoc-create 'ert--print-test-for-ewoc nil nil t)))
+          (set (make-local-variable 'ert--results-ewoc) ewoc)
+          (set (make-local-variable 'ert--results-stats) stats)
+          (set (make-local-variable 'ert--results-progress-bar-string)
+               (make-string (ert-stats-total stats)
+                            (ert-char-for-test-result nil t)))
+          (set (make-local-variable 'ert--results-listener) listener)
+          (loop for test across (ert--stats-tests stats) do
+                (ewoc-enter-last ewoc
+                                 (make-ert--ewoc-entry :test test :hidden-p t)))
+          (ert--results-update-ewoc-hf ert--results-ewoc ert--results-stats)
+          (goto-char (1- (point-max)))
+          buffer)))))
+
+
+(defvar ert--selector-history nil
+  "List of recent test selectors read from terminal.")
+
+;; Should OUTPUT-BUFFER-NAME and MESSAGE-FN really be arguments here?
+;; They are needed only for our automated self-tests at the moment.
+;; Or should there be some other mechanism?
+;;;###autoload
+(defun ert-run-tests-interactively (selector
+                                    &optional output-buffer-name message-fn)
+  "Run the tests specified by SELECTOR and display the results in a buffer.
+
+SELECTOR works as described in `ert-select-tests'.
+OUTPUT-BUFFER-NAME and MESSAGE-FN should normally be nil; they
+are used for automated self-tests and specify which buffer to use
+and how to display message."
+  (interactive
+   (list (let ((default (if ert--selector-history
+                            ;; Can't use `first' here as this form is
+                            ;; not compiled, and `first' is not
+                            ;; defined without cl.
+                            (car ert--selector-history)
+                          "t")))
+           (read-from-minibuffer (if (null default)
+                                     "Run tests: "
+                                   (format "Run tests (default %s): " default))
+                                 nil nil t 'ert--selector-history
+                                 default nil))
+         nil))
+  (unless message-fn (setq message-fn 'message))
+  (lexical-let ((output-buffer-name output-buffer-name)
+                buffer
+                listener
+                (message-fn message-fn))
+    (setq listener
+          (lambda (event-type &rest event-args)
+            (ecase event-type
+              (run-started
+               (destructuring-bind (stats) event-args
+                 (setq buffer (ert--setup-results-buffer stats
+                                                         listener
+                                                         output-buffer-name))
+                 (pop-to-buffer buffer)))
+              (run-ended
+               (destructuring-bind (stats abortedp) event-args
+                 (funcall message-fn
+                          "%sRan %s tests, %s results were as expected%s"
+                          (if (not abortedp)
+                              ""
+                            "Aborted: ")
+                          (ert-stats-total stats)
+                          (ert-stats-completed-expected stats)
+                          (let ((unexpected
+                                 (ert-stats-completed-unexpected stats)))
+                            (if (zerop unexpected)
+                                ""
+                              (format ", %s unexpected" unexpected))))
+                 (ert--results-update-stats-display (with-current-buffer buffer
+                                                      ert--results-ewoc)
+                                                    stats)))
+              (test-started
+               (destructuring-bind (stats test) event-args
+                 (with-current-buffer buffer
+                   (let* ((ewoc ert--results-ewoc)
+                          (pos (ert--stats-test-pos stats test))
+                          (node (ewoc-nth ewoc pos)))
+                     (assert node)
+                     (setf (ert--ewoc-entry-test (ewoc-data node)) test)
+                     (aset ert--results-progress-bar-string pos
+                           (ert-char-for-test-result nil t))
+                     (ert--results-update-stats-display-maybe ewoc stats)
+                     (ewoc-invalidate ewoc node)))))
+              (test-ended
+               (destructuring-bind (stats test result) event-args
+                 (with-current-buffer buffer
+                   (let* ((ewoc ert--results-ewoc)
+                          (pos (ert--stats-test-pos stats test))
+                          (node (ewoc-nth ewoc pos)))
+                     (when (ert--ewoc-entry-hidden-p (ewoc-data node))
+                       (setf (ert--ewoc-entry-hidden-p (ewoc-data node))
+                             (ert-test-result-expected-p test result)))
+                     (aset ert--results-progress-bar-string pos
+                           (ert-char-for-test-result result
+                                                     (ert-test-result-expected-p
+                                                      test result)))
+                     (ert--results-update-stats-display-maybe ewoc stats)
+                     (ewoc-invalidate ewoc node))))))))
+    (ert-run-tests
+     selector
+     listener)))
+;;;###autoload
+(defalias 'ert 'ert-run-tests-interactively)
+
+
+;;; Simple view mode for auxiliary information like stack traces or
+;;; messages.  Mainly binds "q" for quit.
+
+(define-derived-mode ert-simple-view-mode fundamental-mode "ERT-View"
+  "Major mode for viewing auxiliary information in ERT.")
+
+(loop for (key binding) in
+      '(("q" quit-window)
+        )
+      do
+      (define-key ert-simple-view-mode-map key binding))
+
+
+;;; Commands and button actions for the results buffer.
+
+(define-derived-mode ert-results-mode fundamental-mode "ERT-Results"
+  "Major mode for viewing results of ERT test runs.")
+
+(loop for (key binding) in
+      '(;; Stuff that's not in the menu.
+        ("\t" forward-button)
+        ([backtab] backward-button)
+        ("j" ert-results-jump-between-summary-and-result)
+        ("q" quit-window)
+        ("L" ert-results-toggle-printer-limits-for-test-at-point)
+        ("n" ert-results-next-test)
+        ("p" ert-results-previous-test)
+        ;; Stuff that is in the menu.
+        ("R" ert-results-rerun-all-tests)
+        ("r" ert-results-rerun-test-at-point)
+        ("d" ert-results-rerun-test-at-point-debugging-errors)
+        ("." ert-results-find-test-at-point-other-window)
+        ("b" ert-results-pop-to-backtrace-for-test-at-point)
+        ("m" ert-results-pop-to-messages-for-test-at-point)
+        ("l" ert-results-pop-to-should-forms-for-test-at-point)
+        ("h" ert-results-describe-test-at-point)
+        ("D" ert-delete-test)
+        ("T" ert-results-pop-to-timings)
+        )
+      do
+      (define-key ert-results-mode-map key binding))
+
+(easy-menu-define ert-results-mode-menu ert-results-mode-map
+  "Menu for `ert-results-mode'."
+  '("ERT Results"
+    ["Re-run all tests" ert-results-rerun-all-tests]
+    "--"
+    ["Re-run test" ert-results-rerun-test-at-point]
+    ["Debug test" ert-results-rerun-test-at-point-debugging-errors]
+    ["Show test definition" ert-results-find-test-at-point-other-window]
+    "--"
+    ["Show backtrace" ert-results-pop-to-backtrace-for-test-at-point]
+    ["Show messages" ert-results-pop-to-messages-for-test-at-point]
+    ["Show `should' forms" ert-results-pop-to-should-forms-for-test-at-point]
+    ["Describe test" ert-results-describe-test-at-point]
+    "--"
+    ["Delete test" ert-delete-test]
+    "--"
+    ["Show execution time of each test" ert-results-pop-to-timings]
+    ))
+
+(define-button-type 'ert--results-progress-bar-button
+  'action #'ert--results-progress-bar-button-action
+  'help-echo "mouse-2, RET: Reveal test result")
+
+(define-button-type 'ert--test-name-button
+  'action #'ert--test-name-button-action
+  'help-echo "mouse-2, RET: Find test definition")
+
+(define-button-type 'ert--results-expand-collapse-button
+  'action #'ert--results-expand-collapse-button-action
+  'help-echo "mouse-2, RET: Expand/collapse test result")
+
+(defun ert--results-test-node-or-null-at-point ()
+  "If point is on a valid ewoc node, return it; return nil otherwise.
+
+To be used in the ERT results buffer."
+  (let* ((ewoc ert--results-ewoc)
+         (node (ewoc-locate ewoc)))
+    ;; `ewoc-locate' will return an arbitrary node when point is on
+    ;; header or footer, or when all nodes are invisible.  So we need
+    ;; to validate its return value here.
+    ;;
+    ;; Update: I'm seeing nil being returned in some cases now,
+    ;; perhaps this has been changed?
+    (if (and node
+             (>= (point) (ewoc-location node))
+             (not (ert--ewoc-entry-hidden-p (ewoc-data node))))
+        node
+      nil)))
+
+(defun ert--results-test-node-at-point ()
+  "If point is on a valid ewoc node, return it; signal an error otherwise.
+
+To be used in the ERT results buffer."
+  (or (ert--results-test-node-or-null-at-point)
+      (error "No test at point")))
+
+(defun ert-results-next-test ()
+  "Move point to the next test.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (ert--results-move (ewoc-locate ert--results-ewoc) 'ewoc-next
+                     "No tests below"))
+
+(defun ert-results-previous-test ()
+  "Move point to the previous test.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (ert--results-move (ewoc-locate ert--results-ewoc) 'ewoc-prev
+                     "No tests above"))
+
+(defun ert--results-move (node ewoc-fn error-message)
+  "Move point from NODE to the previous or next node.
+
+EWOC-FN specifies the direction and should be either `ewoc-prev'
+or `ewoc-next'.  If there are no more nodes in that direction, an
+error is signalled with the message ERROR-MESSAGE."
+  (loop
+   (setq node (funcall ewoc-fn ert--results-ewoc node))
+   (when (null node)
+     (error "%s" error-message))
+   (unless (ert--ewoc-entry-hidden-p (ewoc-data node))
+     (goto-char (ewoc-location node))
+     (return))))
+
+(defun ert--results-expand-collapse-button-action (button)
+  "Expand or collapse the test node BUTTON belongs to."
+  (let* ((ewoc ert--results-ewoc)
+         (node (save-excursion
+                 (goto-char (ert--button-action-position))
+                 (ert--results-test-node-at-point)))
+         (entry (ewoc-data node)))
+    (setf (ert--ewoc-entry-expanded-p entry)
+          (not (ert--ewoc-entry-expanded-p entry)))
+    (ewoc-invalidate ewoc node)))
+
+(defun ert-results-find-test-at-point-other-window ()
+  "Find the definition of the test at point in another window.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (let ((name (ert-test-at-point)))
+    (unless name
+      (error "No test at point"))
+    (ert-find-test-other-window name)))
+
+(defun ert--test-name-button-action (button)
+  "Find the definition of the test BUTTON belongs to, in another window."
+  (let ((name (button-get button 'ert-test-name)))
+    (ert-find-test-other-window name)))
+
+(defun ert--ewoc-position (ewoc node)
+  ;; checkdoc-order: nil
+  "Return the position of NODE in EWOC, or nil if NODE is not in EWOC."
+  (loop for i from 0
+        for node-here = (ewoc-nth ewoc 0) then (ewoc-next ewoc node-here)
+        do (when (eql node node-here)
+             (return i))
+        finally (return nil)))
+
+(defun ert-results-jump-between-summary-and-result ()
+  "Jump back and forth between the test run summary and individual test results.
+
+From an ewoc node, jumps to the character that represents the
+same test in the progress bar, and vice versa.
+
+To be used in the ERT results buffer."
+  ;; Maybe this command isn't actually needed much, but if it is, it
+  ;; seems like an indication that the UI design is not optimal.  If
+  ;; jumping back and forth between a summary at the top of the buffer
+  ;; and the error log in the remainder of the buffer is useful, then
+  ;; the summary apparently needs to be easily accessible from the
+  ;; error log, and perhaps it would be better to have it in a
+  ;; separate buffer to keep it visible.
+  (interactive)
+  (let ((ewoc ert--results-ewoc)
+        (progress-bar-begin ert--results-progress-bar-button-begin))
+    (cond ((ert--results-test-node-or-null-at-point)
+           (let* ((node (ert--results-test-node-at-point))
+                  (pos (ert--ewoc-position ewoc node)))
+             (goto-char (+ progress-bar-begin pos))))
+          ((and (<= progress-bar-begin (point))
+                (< (point) (button-end (button-at progress-bar-begin))))
+           (let* ((node (ewoc-nth ewoc (- (point) progress-bar-begin)))
+                  (entry (ewoc-data node)))
+             (when (ert--ewoc-entry-hidden-p entry)
+               (setf (ert--ewoc-entry-hidden-p entry) nil)
+               (ewoc-invalidate ewoc node))
+             (ewoc-goto-node ewoc node)))
+          (t
+           (goto-char progress-bar-begin)))))
+
+(defun ert-test-at-point ()
+  "Return the name of the test at point as a symbol, or nil if none."
+  (or (and (eql major-mode 'ert-results-mode)
+           (let ((test (ert--results-test-at-point-no-redefinition)))
+             (and test (ert-test-name test))))
+      (let* ((thing (thing-at-point 'symbol))
+             (sym (intern-soft thing)))
+        (and (ert-test-boundp sym)
+             sym))))
+
+(defun ert--results-test-at-point-no-redefinition ()
+  "Return the test at point, or nil.
+
+To be used in the ERT results buffer."
+  (assert (eql major-mode 'ert-results-mode))
+  (if (ert--results-test-node-or-null-at-point)
+      (let* ((node (ert--results-test-node-at-point))
+             (test (ert--ewoc-entry-test (ewoc-data node))))
+        test)
+    (let ((progress-bar-begin ert--results-progress-bar-button-begin))
+      (when (and (<= progress-bar-begin (point))
+                 (< (point) (button-end (button-at progress-bar-begin))))
+        (let* ((test-index (- (point) progress-bar-begin))
+               (test (aref (ert--stats-tests ert--results-stats)
+                           test-index)))
+          test)))))
+
+(defun ert--results-test-at-point-allow-redefinition ()
+  "Look up the test at point, and check whether it has been redefined.
+
+To be used in the ERT results buffer.
+
+Returns a list of two elements: the test (or nil) and a symbol
+specifying whether the test has been redefined.
+
+If a new test has been defined with the same name as the test at
+point, replaces the test at point with the new test, and returns
+the new test and the symbol `redefined'.
+
+If the test has been deleted, returns the old test and the symbol
+`deleted'.
+
+If the test is still current, returns the test and the symbol nil.
+
+If there is no test at point, returns a list with two nils."
+  (let ((test (ert--results-test-at-point-no-redefinition)))
+    (cond ((null test)
+           `(nil nil))
+          ((null (ert-test-name test))
+           `(,test nil))
+          (t
+           (let* ((name (ert-test-name test))
+                  (new-test (and (ert-test-boundp name)
+                                 (ert-get-test name))))
+             (cond ((eql test new-test)
+                    `(,test nil))
+                   ((null new-test)
+                    `(,test deleted))
+                   (t
+                    (ert--results-update-after-test-redefinition
+                     (ert--stats-test-pos ert--results-stats test)
+                     new-test)
+                    `(,new-test redefined))))))))
+
+(defun ert--results-update-after-test-redefinition (pos new-test)
+  "Update results buffer after the test at pos POS has been redefined.
+
+Also updates the stats object.  NEW-TEST is the new test
+definition."
+  (let* ((stats ert--results-stats)
+         (ewoc ert--results-ewoc)
+         (node (ewoc-nth ewoc pos))
+         (entry (ewoc-data node)))
+    (ert--stats-set-test-and-result stats pos new-test nil)
+    (setf (ert--ewoc-entry-test entry) new-test
+          (aref ert--results-progress-bar-string pos) (ert-char-for-test-result
+                                                       nil t))
+    (ewoc-invalidate ewoc node))
+  nil)
+
+(defun ert--button-action-position ()
+  "The buffer position where the last button action was triggered."
+  (cond ((integerp last-command-event)
+         (point))
+        ((eventp last-command-event)
+         (posn-point (event-start last-command-event)))
+        (t (assert nil))))
+
+(defun ert--results-progress-bar-button-action (button)
+  "Jump to details for the test represented by the character clicked in BUTTON."
+  (goto-char (ert--button-action-position))
+  (ert-results-jump-between-summary-and-result))
+
+(defun ert-results-rerun-all-tests ()
+  "Re-run all tests, using the same selector.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (assert (eql major-mode 'ert-results-mode))
+  (let ((selector (ert--stats-selector ert--results-stats)))
+    (ert-run-tests-interactively selector (buffer-name))))
+
+(defun ert-results-rerun-test-at-point ()
+  "Re-run the test at point.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (destructuring-bind (test redefinition-state)
+      (ert--results-test-at-point-allow-redefinition)
+    (when (null test)
+      (error "No test at point"))
+    (let* ((stats ert--results-stats)
+           (progress-message (format "Running %stest %S"
+                                     (ecase redefinition-state
+                                       ((nil) "")
+                                       (redefined "new definition of ")
+                                       (deleted "deleted "))
+                                     (ert-test-name test))))
+      ;; Need to save and restore point manually here: When point is on
+      ;; the first visible ewoc entry while the header is updated, point
+      ;; moves to the top of the buffer.  This is undesirable, and a
+      ;; simple `save-excursion' doesn't prevent it.
+      (let ((point (point)))
+        (unwind-protect
+            (unwind-protect
+                (progn
+                  (message "%s..." progress-message)
+                  (ert-run-or-rerun-test stats test
+                                         ert--results-listener))
+              (ert--results-update-stats-display ert--results-ewoc stats)
+              (message "%s...%s"
+                       progress-message
+                       (let ((result (ert-test-most-recent-result test)))
+                         (ert-string-for-test-result
+                          result (ert-test-result-expected-p test result)))))
+          (goto-char point))))))
+
+(defun ert-results-rerun-test-at-point-debugging-errors ()
+  "Re-run the test at point with `ert-debug-on-error' bound to t.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (let ((ert-debug-on-error t))
+    (ert-results-rerun-test-at-point)))
+
+(defun ert-results-pop-to-backtrace-for-test-at-point ()
+  "Display the backtrace for the test at point.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (let* ((test (ert--results-test-at-point-no-redefinition))
+         (stats ert--results-stats)
+         (pos (ert--stats-test-pos stats test))
+         (result (aref (ert--stats-test-results stats) pos)))
+    (etypecase result
+      (ert-test-passed (error "Test passed, no backtrace available"))
+      (ert-test-result-with-condition
+       (let ((backtrace (ert-test-result-with-condition-backtrace result))
+             (buffer (get-buffer-create "*ERT Backtrace*")))
+         (pop-to-buffer buffer)
+         (setq buffer-read-only t)
+         (let ((inhibit-read-only t))
+           (buffer-disable-undo)
+           (erase-buffer)
+           (ert-simple-view-mode)
+           ;; Use unibyte because `debugger-setup-buffer' also does so.
+           (set-buffer-multibyte nil)
+           (setq truncate-lines t)
+           (ert--print-backtrace backtrace)
+           (debugger-make-xrefs)
+           (goto-char (point-min))
+           (insert "Backtrace for test `")
+           (ert-insert-test-name-button (ert-test-name test))
+           (insert "':\n")))))))
+
+(defun ert-results-pop-to-messages-for-test-at-point ()
+  "Display the part of the *Messages* buffer generated during the test at point.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (let* ((test (ert--results-test-at-point-no-redefinition))
+         (stats ert--results-stats)
+         (pos (ert--stats-test-pos stats test))
+         (result (aref (ert--stats-test-results stats) pos)))
+    (let ((buffer (get-buffer-create "*ERT Messages*")))
+      (pop-to-buffer buffer)
+      (setq buffer-read-only t)
+      (let ((inhibit-read-only t))
+        (buffer-disable-undo)
+        (erase-buffer)
+        (ert-simple-view-mode)
+        (insert (ert-test-result-messages result))
+        (goto-char (point-min))
+        (insert "Messages for test `")
+        (ert-insert-test-name-button (ert-test-name test))
+        (insert "':\n")))))
+
+(defun ert-results-pop-to-should-forms-for-test-at-point ()
+  "Display the list of `should' forms executed during the test at point.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (let* ((test (ert--results-test-at-point-no-redefinition))
+         (stats ert--results-stats)
+         (pos (ert--stats-test-pos stats test))
+         (result (aref (ert--stats-test-results stats) pos)))
+    (let ((buffer (get-buffer-create "*ERT list of should forms*")))
+      (pop-to-buffer buffer)
+      (setq buffer-read-only t)
+      (let ((inhibit-read-only t))
+        (buffer-disable-undo)
+        (erase-buffer)
+        (ert-simple-view-mode)
+        (if (null (ert-test-result-should-forms result))
+            (insert "\n(No should forms during this test.)\n")
+          (loop for form-description in (ert-test-result-should-forms result)
+                for i from 1 do
+                (insert "\n")
+                (insert (format "%s: " i))
+                (let ((begin (point)))
+                  (ert--pp-with-indentation-and-newline form-description)
+                  (ert--make-xrefs-region begin (point)))))
+        (goto-char (point-min))
+        (insert "`should' forms executed during test `")
+        (ert-insert-test-name-button (ert-test-name test))
+        (insert "':\n")
+        (insert "\n")
+        (insert (concat "(Values are shallow copies and may have "
+                        "looked different during the test if they\n"
+                        "have been modified destructively.)\n"))
+        (forward-line 1)))))
+
+(defun ert-results-toggle-printer-limits-for-test-at-point ()
+  "Toggle how much of the condition to print for the test at point.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (let* ((ewoc ert--results-ewoc)
+         (node (ert--results-test-node-at-point))
+         (entry (ewoc-data node)))
+    (setf (ert--ewoc-entry-extended-printer-limits-p entry)
+          (not (ert--ewoc-entry-extended-printer-limits-p entry)))
+    (ewoc-invalidate ewoc node)))
+
+(defun ert-results-pop-to-timings ()
+  "Display test timings for the last run.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (let* ((stats ert--results-stats)
+         (start-times (ert--stats-test-start-times stats))
+         (end-times (ert--stats-test-end-times stats))
+         (buffer (get-buffer-create "*ERT timings*"))
+         (data (loop for test across (ert--stats-tests stats)
+                     for start-time across (ert--stats-test-start-times stats)
+                     for end-time across (ert--stats-test-end-times stats)
+                     collect (list test
+                                   (float-time (subtract-time end-time
+                                                              start-time))))))
+    (setq data (sort data (lambda (a b)
+                            (> (second a) (second b)))))
+    (pop-to-buffer buffer)
+    (setq buffer-read-only t)
+    (let ((inhibit-read-only t))
+      (buffer-disable-undo)
+      (erase-buffer)
+      (ert-simple-view-mode)
+      (if (null data)
+          (insert "(No data)\n")
+        (insert (format "%-3s  %8s %8s\n" "" "time" "cumul"))
+        (loop for (test time) in data
+              for cumul-time = time then (+ cumul-time time)
+              for i from 1 do
+              (let ((begin (point)))
+                (insert (format "%3s: %8.3f %8.3f " i time cumul-time))
+                (ert-insert-test-name-button (ert-test-name test))
+                (insert "\n"))))
+      (goto-char (point-min))
+      (insert "Tests by run time (seconds):\n\n")
+      (forward-line 1))))
+
+;;;###autoload
+(defun ert-describe-test (test-or-test-name)
+  "Display the documentation for TEST-OR-TEST-NAME (a symbol or ert-test)."
+  (interactive (list (ert-read-test-name-at-point "Describe test")))
+  (when (< emacs-major-version 24)
+    (error "Requires Emacs 24"))
+  (let (test-name
+        test-definition)
+    (etypecase test-or-test-name
+      (symbol (setq test-name test-or-test-name
+                    test-definition (ert-get-test test-or-test-name)))
+      (ert-test (setq test-name (ert-test-name test-or-test-name)
+                      test-definition test-or-test-name)))
+    (help-setup-xref (list #'ert-describe-test test-or-test-name)
+                     (called-interactively-p 'interactive))
+    (save-excursion
+      (with-help-window (help-buffer)
+        (with-current-buffer (help-buffer)
+          (insert (if test-name (format "%S" test-name) "<anonymous test>"))
+          (insert " is a test")
+          (let ((file-name (and test-name
+                                (symbol-file test-name 'ert-deftest))))
+            (when file-name
+              (insert " defined in `" (file-name-nondirectory file-name) "'")
+              (save-excursion
+                (re-search-backward "`\\([^`']+\\)'" nil t)
+                (help-xref-button 1 'help-function-def test-name file-name)))
+            (insert ".")
+            (fill-region-as-paragraph (point-min) (point))
+            (insert "\n\n")
+            (unless (and (ert-test-boundp test-name)
+                         (eql (ert-get-test test-name) test-definition))
+              (let ((begin (point)))
+                (insert "Note: This test has been redefined or deleted, "
+                        "this documentation refers to an old definition.")
+                (fill-region-as-paragraph begin (point)))
+              (insert "\n\n"))
+            (insert (or (ert-test-documentation test-definition)
+                        "It is not documented.")
+                    "\n")))))))
+
+(defun ert-results-describe-test-at-point ()
+  "Display the documentation of the test at point.
+
+To be used in the ERT results buffer."
+  (interactive)
+  (ert-describe-test (ert--results-test-at-point-no-redefinition)))
+
+
+;;; Actions on load/unload.
+
+(add-to-list 'find-function-regexp-alist '(ert-deftest . ert--find-test-regexp))
+(add-to-list 'minor-mode-alist '(ert--current-run-stats
+                                 (:eval
+                                  (ert--tests-running-mode-line-indicator))))
+(add-to-list 'emacs-lisp-mode-hook 'ert--activate-font-lock-keywords)
+
+(defun ert--unload-function ()
+  "Unload function to undo the side-effects of loading ert.el."
+  (ert--remove-from-list 'find-function-regexp-alist 'ert-deftest :key #'car)
+  (ert--remove-from-list 'minor-mode-alist 'ert--current-run-stats :key #'car)
+  (ert--remove-from-list 'emacs-lisp-mode-hook
+                         'ert--activate-font-lock-keywords)
+  nil)
+
+(defvar ert-unload-hook '())
+(add-hook 'ert-unload-hook 'ert--unload-function)
+
+
+(provide 'ert)
+
+;;; ert.el ends here