completion: add comment for test_completion()

diff --git a/t/t4040-whitespace-status.sh b/t/t4040-whitespace-status.sh
index abc49348b196cf0fec232b6f2399356e4fe324d5..3c728a3ebf9ce52e5c24c81525d5cb749cfb2957 100755 (executable)
--- a/t/t4040-whitespace-status.sh
+++ b/t/t4040-whitespace-status.sh
@@ -67,4 +67,9 @@ test_expect_success 'diff-files --diff-filter --quiet' '
        test_must_fail git diff-files --diff-filter=M --quiet
 '
 
+test_expect_success 'diff-tree --diff-filter --quiet' '
+       git commit -a -m "worktree state" &&
+       test_must_fail git diff-tree --diff-filter=M --quiet HEAD^ HEAD
+'
+
 test_done