tests: introduce test_must_fail

When we expect a git command to notice and signal errors, we
carelessly wrote in our tests:

    test_expect_success 'reject bogus request' '
        do something &&
        do something else &&
        ! git command
    '

but a non-zero exit could come from the "git command" segfaulting.

A new helper function "tset_must_fail" is introduced and it is
meant to be used to make sure the command gracefully fails (iow,
dying and exiting with non zero status is counted as a failure
to "gracefully fail").  The above example should be written as:

    test_expect_success 'reject bogus request' '
        do something &&
        do something else &&
        test_must_fail git command
    '

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

1 files changed, 17 insertions, 0 deletions

diff --git a/t/test-lib.sh b/t/test-lib.sh
index 142540e..c0c5e21 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -257,6 +257,23 @@ test_expect_code () {
 	echo >&3 ""
 }
 
+# This is not among top-level (test_expect_success | test_expect_failure)
+# but is a prefix that can be used in the test script, like:
+#
+#	test_expect_success 'complain and die' '
+#           do something &&
+#           do something else &&
+#	    test_must_fail git checkout ../outerspace
+#	'
+#
+# Writing this as "! git checkout ../outerspace" is wrong, because
+# the failure could be due to a segv.  We want a controlled failure.
+
+test_must_fail () {
+	"$@"
+	test $? -gt 0 -a $? -le 128
+}
+
 # Most tests can use the created repository, but some may need to create more.
 # Usage: test_create_repo <directory>
 test_create_repo () {