test_expect_success 'force diff with "diff"' '
echo >.gitattributes "file diff" &&
git diff >actual &&
+ test_cmp "$TEST_DIRECTORY"/t4020/diff.NUL actual
+'
+
+test_expect_success 'diff --cached' '
+ git add file &&
+ git update-index --assume-unchanged file &&
+ echo second >file &&
+ git diff --cached >actual &&
test_cmp ../t4020/diff.NUL actual
'