t3600: test behavior of reverse-d/f conflict

The previous commit taught "rm" that it is safe to consider
"d/f" removed when "d" has become a non-directory. This
patch adds a test for the opposite: a file "d" that becomes
a directory.

In this case, "git rm" does need to complain, because we
should not be removing arbitrary content under "d". Git
already behaves correctly, but let's make sure that remains
the case by protecting the behavior with a test.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3600-rm.sh

@@ -647,4 +647,16 @@ test_expect_success SYMLINKS 'rm of d/f when d has become a dangling symlink' '
 	test_path_is_missing d
 '
 
+test_expect_success 'rm of file when it has become a directory' '
+	rm -rf d &&
+	>d &&
+	git add d &&
+	rm -f d &&
+	mkdir d &&
+	>d/f &&
+	test_must_fail git rm d &&
+	git rev-parse --verify :d &&
+	test_path_is_file d/f
+'
+
 test_done