t/t3800-mktag.sh: use test_must_fail rather than '!'

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

diff --git a/t/t3800-mktag.sh b/t/t3800-mktag.sh
index f2803206f1b170adef4e05d3aa46b01084adf470..bdc6e132cacbccc72a903c1aad1bbfe1364471ab 100755 (executable)
--- a/t/t3800-mktag.sh
+++ b/t/t3800-mktag.sh
@@ -14,8 +14,8 @@ test_description='git-mktag: tag object verify test'
 check_verify_failure () {
        expect="$2"
        test_expect_success "$1" '
-               ( ! git-mktag <tag.sig 2>message ) &&
-               grep -q "$expect" message
+               ( test_must_fail git-mktag <tag.sig 2>message ) &&
+               grep "$expect" message
        '
 }