Switch from tox to nox

Recent tox releases have put us on a config treadmill. Avoid these
issues entirely by using nox. Nox is a tox alternative that uses
standard tools like pip and should be simpler to use for us.

Change-Id: Ie79845bbed7ca1254aec466bd5219186fefcdac9

7 files changed, 83 insertions, 62 deletions

diff --git a/.gitignore b/.gitignore
index 11600e3..38ca662 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,7 @@ ChangeLog
 .gerrit
 .testrepository
 .tox
+.nox
 .venv
 *.egg
 *.egg-info
diff --git a/.zuul.yaml b/.zuul.yaml
index b487336..7a5a062 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -2,18 +2,18 @@
     vars:
       release_python: python3
     templates:
-      - publish-opendev-tox-docs
+      - publish-opendev-nox-docs
     check:
       jobs: &jobs
         - build-python-release
-        - tox-linters
-        - tox-py36:
+        - nox-linters
+        - nox-py36:
             nodeset: ubuntu-bionic
-        - tox-py37:
+        - nox-py37:
             nodeset: ubuntu-bionic
-        - tox-py38:
+        - nox-py38:
             nodeset: ubuntu-focal
-        - tox-py39:
+        - nox-py39:
             nodeset: ubuntu-focal
     gate:
       jobs: *jobs
@@ -23,4 +23,4 @@
     release:
       jobs:
         - opendev-release-python
-        - opendev-publish-unversioned-tox-docs
+        - opendev-publish-unversioned-nox-docs
diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
index 9b43ec7..7877dce 100644
--- a/CONTRIBUTING.rst
+++ b/CONTRIBUTING.rst
@@ -20,13 +20,13 @@ tools, or review ``bindep.txt`` by hand.
 Running Tests
 -------------
 
-The testing system is based on a combination of tox and testr. The canonical
-approach to running tests is to simply run the command `tox`. This will
+The testing system is based on a combination of nox and testr. The canonical
+approach to running tests is to simply run the command `nox`. This will
 create virtual environments, populate them with dependencies and run all of
-the tests that OpenStack CI systems run. Behind the scenes, tox is running
-`testr run --parallel`, but is set up such that you can supply any additional
-testr arguments that are needed to tox. For example, you can run:
-`tox -- --analyze-isolation` to cause tox to tell testr to add
+the tests that OpenStack CI systems run. Behind the scenes, nox is running
+`stestr run`, but is set up such that you can supply any additional
+stestr arguments that are needed to nox. For example, you can run:
+`nox -s tests -- --analyze-isolation` to cause nox to tell testr to add
 --analyze-isolation to its argument list.
 
 It is also possible to run the tests inside of a virtual environment
@@ -38,7 +38,6 @@ test-requirements.txt. Installing them via pip, for instance, is simply::
   pip install -r requirements.txt -r test-requirements.txt
 
 In you go this route, you can interact with the testr command directly.
-Running `testr run` will run the entire test suite. `testr run --parallel`
-will run it in parallel (this is the default incantation tox uses.) More
-information about testr can be found at:
-https://testrepository.readthedocs.io/en/latest/
+Running `stestr run` will run the entire test suite.
+More information about testr can be found at:
+https://stestr.readthedocs.io/en/latest/README.html
diff --git a/doc/source/developing.rst b/doc/source/developing.rst
index fa2c2a1..81d4cf5 100644
--- a/doc/source/developing.rst
+++ b/doc/source/developing.rst
@@ -13,7 +13,7 @@ following:
   cached copy (it needs to be located in a ``.gerrit`` directory at the
   top level of the git-review project)
 
-To run git-review integration tests, use tox. For example, to test against
-Python 3.7::
+To run git-review integration tests, use nox. For example, to test against
+Python 3::
 
-    tox -e py37
+    nox -s tests
diff --git a/noxfile.py b/noxfile.py
new file mode 100644
index 0000000..aa20c0e
--- /dev/null
+++ b/noxfile.py
@@ -0,0 +1,58 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License.  You may obtain
+# a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import nox
+
+
+nox.options.error_on_external_run = True
+nox.options.reuse_existing_virtualenvs = True
+nox.options.sessions = ["tests-3", "docs", "linters"]
+
+
+@nox.session(python="3")
+def linters(session):
+    session.install("-r", "requirements.txt")
+    session.install("-r", "test-requirements.txt")
+    session.install("-e", ".")
+    session.run("flake8")
+
+
+@nox.session(python="3")
+def docs(session):
+    session.install("-r", "requirements.txt")
+    session.install("-r", "doc/requirements.txt")
+    session.install("-e", ".")
+    session.run(
+        "sphinx-build", "-W",
+        "-d", "doc/build/doctrees",
+        "-b", "html",
+        "doc/source/", "doc/build/html"
+    )
+
+
+@nox.session(python="3")
+def venv(session):
+    session.install("-r", "requirements.txt")
+    session.install("-r", "test-requirements.txt")
+    session.install("-e", ".")
+    session.run(*session.posargs)
+
+
+@nox.session(python="3")
+def tests(session):
+    session.install("-r", "requirements.txt")
+    session.install("-r", "test-requirements.txt")
+    session.install("-e", ".")
+    session.run("python", "-m", "git_review.tests.check_test_id_hashes",
+                "discover", "--list")
+    session.run("python", "-m", "git_review.tests.prepare")
+    session.run("stestr", "run", "--color", *session.posargs)
diff --git a/setup.cfg b/setup.cfg
index f563032..8bef32d 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -42,3 +42,8 @@ console_scripts =
 [pbr]
 manpages =
     git-review.1
+
+[flake8]
+ignore = E125,H202,H405,H904,W504
+show-source = true
+exclude = .venv,.git,.tox,.nox,dist,doc,releasenotes,*lib/python*,*egg,build
diff --git a/tox.ini b/tox.ini
deleted file mode 100644
index 3543c94..0000000
--- a/tox.ini
+++ /dev/null
@@ -1,42 +0,0 @@
-[tox]
-envlist = linters,docs,py3
-ignore_basepython_conflict = true
-
-[testenv]
-basepython = python3
-usedevelop = true
-# See "testing behind a proxy" https://review.opendev.org/624496
-passenv =
-  http_proxy
-  https_proxy
-  # avoids potential slip-over of java 1.9 which breaks Gerrit, without it
-  # Gerrit may start with incompatible java version.
-  JAVA_HOME
-  # uncomment to allow custom java options to be added
-  # _JAVA_OPTIONS
-  TERM
-commands =
-  python -m git_review.tests.check_test_id_hashes discover --list
-  python -m git_review.tests.prepare
-  stestr run --color {posargs}
-deps =
-  -r{toxinidir}/requirements.txt
-  -r{toxinidir}/test-requirements.txt
-
-[testenv:linters]
-commands = flake8
-
-[testenv:docs]
-deps =
-  -r{toxinidir}/requirements.txt
-  -r{toxinidir}/doc/requirements.txt
-commands =
-  sphinx-build -W -d doc/build/doctrees -b html doc/source/ doc/build/html
-
-[testenv:venv]
-commands = {posargs}
-
-[flake8]
-ignore = E125,H202,H405,H904,W504
-show-source = true
-exclude = .venv,.git,.tox,dist,doc,releasenotes,*lib/python*,*egg,build