t7800: don't rely on reuse_worktree_file()

A test in t7800 tries to make sure that when git-difftool runs an
external tool that fails, it stops looking at files. Our fake failing
tool prints the file name it was asked to diff before exiting non-zero,
and then we confirm the output contains only that file.

However, this subtly relies on our internal reuse_worktree_file().
Because we're diffing between branches, the command run by difftool
might see:

  - the git-stored filename (e.g., "file"), if we decided that the
    working tree contents were up-to-date with the object in the index
    and HEAD, and we could reuse them

  - a temporary filename (e.g. "/tmp/abc123_file") if we had to dump the
    contents from the object database

If the latter case happens, then the test fails, because it's expecting
the string "file". I discovered this when debugging something unrelated
with reuse_worktree_file(). I _thought_ it should be able to be
triggered by a racy-git situation, but running:

  ./t7800-difftool.sh --stress --run=2,13

never seems to fail. However, by my reading of reuse_worktree_file(),
this would probably always fail under Cygwin, because it sets
NO_FAST_WORKING_DIRECTORY. At any rate, since reuse_worktree_file()
is meant to be an optimization that may or may not trigger, our test
should be robust either way.

Instead of checking the filename, let's just make sure we got a single
line of output (which would not be true if we continued after the first
failure).

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

diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 6bac9ed180e7342b34401b2d6af9e83b4472f08d..29b92907e2ad850514fe970ca1adeeda8d0697c8 100755 (executable)
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -125,15 +125,14 @@ test_expect_success 'difftool stops on error with --trust-exit-code' '
        test_when_finished "rm -f for-diff .git/fail-right-file" &&
        test_when_finished "git reset -- for-diff" &&
        write_script .git/fail-right-file <<-\EOF &&
-       echo "$2"
+       echo failed
        exit 1
        EOF
        >for-diff &&
        git add for-diff &&
-       echo file >expect &&
        test_must_fail git difftool -y --trust-exit-code \
                --extcmd .git/fail-right-file branch >actual &&
-       test_cmp expect actual
+       test_line_count = 1 actual
 '
 
 test_expect_success 'difftool honors exit status if command not found' '