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, 6 insertions, 8 deletions

diff --git a/t/README b/t/README
index 36f251761..73ed11bfe 100644
--- a/t/README
+++ b/t/README
@@ -160,14 +160,12 @@ library for your script to use.
 
  - test_expect_failure <message> <script>
 
-   This is the opposite of test_expect_success.  If <script>
-   yields success, test is considered a failure.
-
-   Example:
-
-	test_expect_failure \
-	    'git-update-index without --add should fail adding.' \
-	    'git-update-index should-be-empty'
+   This is NOT the opposite of test_expect_success, but is used
+   to mark a test that demonstrates a known breakage.  Unlike
+   the usual test_expect_success tests, which say "ok" on
+   success and "FAIL" on failure, this will say "FIXED" on
+   success and "still broken" on failure.  Failures from these
+   tests won't cause -i (immediate) to stop.
 
  - test_debug <script>