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

diff --git a/t/t4000-diff-format.sh b/t/t4000-diff-format.sh
index 7d92ae3e996b31f8fa9e0b62f40a04ec1940cf70..c44b27aeb24816a346f0aa84d70546a0ffd83b2a 100755 (executable)
--- a/t/t4000-diff-format.sh
+++ b/t/t4000-diff-format.sh
@@ -16,7 +16,7 @@ cat path0 >path1
 chmod +x path1
 
 test_expect_success \
-    'update-cache --add two files with and without +x.' \
+    'update-index --add two files with and without +x.' \
     'git update-index --add path0 path1'
 
 mv path0 path0-