add test_cmp function for test scripts

Many scripts compare actual and expected output using
"diff -u". This is nicer than "cmp" because the output shows
how the two differ. However, not all versions of diff
understand -u, leading to unnecessary test failure.

This adds a test_cmp function to the test scripts and
switches all "diff -u" invocations to use it. The function
uses the contents of "$GIT_TEST_CMP" to compare its
arguments; the default is "diff -u".

On systems with a less-capable diff, you can do:

  GIT_TEST_CMP=cmp make test

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/t/test-lib.sh b/t/test-lib.sh
index 6aea0ea0a5..268b26c959 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -42,6 +42,7 @@ export GIT_MERGE_VERBOSITY
 export GIT_AUTHOR_EMAIL GIT_AUTHOR_NAME
 export GIT_COMMITTER_EMAIL GIT_COMMITTER_NAME
 export EDITOR VISUAL
+GIT_TEST_CMP=${GIT_TEST_CMP:-diff -u}
 
 # Protect ourselves from common misconfiguration to export
 # CDPATH into the environment
@@ -302,6 +303,23 @@ test_must_fail () {
 	test $? -gt 0 -a $? -le 128
 }
 
+# test_cmp is a helper function to compare actual and expected output.
+# You can use it like:
+#
+#	test_expect_success 'foo works' '
+#		echo expected >expected &&
+#		foo >actual &&
+#		test_cmp expected actual
+#	'
+#
+# This could be written as either "cmp" or "diff -u", but:
+# - cmp's output is not nearly as easy to read as diff -u
+# - not all diff versions understand "-u"
+
+test_cmp() {
+	$GIT_TEST_CMP "$@"
+}
+
 # Most tests can use the created repository, but some may need to create more.
 # Usage: test_create_repo <directory>
 test_create_repo () {