Sane use of test_expect_failure

Originally, test_expect_failure was designed to be the opposite
of test_expect_success, but this was a bad decision.  Most tests
run a series of commands that leads to the single command that
needs to be tested, like this:

    test_expect_{success,failure} 'test title' '
	setup1 &&
        setup2 &&
        setup3 &&
        what is to be tested
    '

And expecting a failure exit from the whole sequence misses the
point of writing tests.  Your setup$N that are supposed to
succeed may have failed without even reaching what you are
trying to test.  The only valid use of test_expect_failure is to
check a trivial single command that is expected to fail, which
is a minority in tests of Porcelain-ish commands.

This large-ish patch rewrites all uses of test_expect_failure to
use test_expect_success and rewrites the condition of what is
tested, like this:

    test_expect_success 'test title' '
	setup1 &&
        setup2 &&
        setup3 &&
        ! this command should fail
    '

test_expect_failure is redefined to serve as a reminder that
that test *should* succeed but due to a known breakage in git it
currently does not pass.  So if git-foo command should create a
file 'bar' but you discovered a bug that it doesn't, you can
write a test like this:

    test_expect_failure 'git-foo should create bar' '
        rm -f bar &&
        git foo &&
        test -f bar
    '

This construct acts similar to test_expect_success, but instead
of reporting "ok/FAIL" like test_expect_success does, the
outcome is reported as "FIXED/still broken".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/t/t2100-update-cache-badpath.sh b/t/t2100-update-cache-badpath.sh
index 04a1ed1a6..9beaecd18 100755
--- a/t/t2100-update-cache-badpath.sh
+++ b/t/t2100-update-cache-badpath.sh
@@ -44,8 +44,8 @@ date >path1/file1
 
 for p in path0/file0 path1/file1 path2 path3
 do
-	test_expect_failure \
+	test_expect_success \
 	    "git update-index to add conflicting path $p should fail." \
-	    "git update-index --add -- $p"
+	    "! git update-index --add -- $p"
 done
 test_done