test-lib-functions: make 'test_cmp_rev' more informative on failure

The 'test_cmp_rev' helper is merely a wrapper around 'test_cmp'
checking the output of two 'git rev-parse' commands, which means that
its output on failure is not particularly informative, as it's
basically two OIDs with a bit of extra clutter of the diff header, but
without any indication of which two revisions have caused the failure:

--- expect.rev  2018-11-17 14:02:11.569747033 +0000
+++ actual.rev  2018-11-17 14:02:11.569747033 +0000
@@ -1 +1 @@
-d79ce1670bdcb76e6d1da2ae095e890ccb326ae9
+139b20d8e6c5b496de61f033f642d0e3dbff528d

It also pollutes the test repo with these two intermediate files,
though that doesn't seem to cause any complications in our current
tests (meaning that I couldn't find any tests that have to work around
the presence of these files by explicitly removing or ignoring them).

Enhance 'test_cmp_rev' to provide a more useful output on failure with
less clutter:

error: two revisions point to different objects:
'HEAD^': d79ce1670bdcb76e6d1da2ae095e890ccb326ae9
'extra': 139b20d8e6c5b496de61f033f642d0e3dbff528d

Doing so is more convenient when storing the OIDs outputted by 'git
rev-parse' in a local variable each, which, as a bonus, won't pollute
the repository with intermediate files.

While at it, also ensure that 'test_cmp_rev' is invoked with the right
number of parameters, namely two.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index b4e391526a2957fe2e578d226ef756321e51aef7..589d93d15b4d7fa3021d34448364981cd7b68bdf 100644 (file)
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -854,9 +854,23 @@ test_must_be_empty () {
 
 # Tests that its two parameters refer to the same revision
 test_cmp_rev () {
-       git rev-parse --verify "$1" >expect.rev &&
-       git rev-parse --verify "$2" >actual.rev &&
-       test_cmp expect.rev actual.rev
+       if test $# != 2
+       then
+               error "bug in the test script: test_cmp_rev requires two revisions, but got $#"
+       else
+               local r1 r2
+               r1=$(git rev-parse --verify "$1") &&
+               r2=$(git rev-parse --verify "$2") &&
+               if test "$r1" != "$r2"
+               then
+                       cat >&4 <<-EOF
+                       error: two revisions point to different objects:
+                         '$1': $r1
+                         '$2': $r2
+                       EOF
+                       return 1
+               fi
+       fi
 }
 
 # Print a sequence of integers in increasing order, either with