t4150: am refuses patches when paused

Since c95b138 (Fix git-am safety checks, 2006-09-15), when there is a
session in progress, git-am will check the command-line arguments and
standard input to ensure that the user does not pass it any patches.

Add a test for this.

Reviewed-by: Stefan Beller <sbeller@google.com>
Reviewed-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4150-am.sh

@@ -397,6 +397,20 @@ test_expect_success 'am --abort removes a stray directory' '
 	test_path_is_missing .git/rebase-apply
 '
 
+test_expect_success 'am refuses patches when paused' '
+	rm -fr .git/rebase-apply &&
+	git reset --hard &&
+	git checkout lorem2^^ &&
+
+	test_must_fail git am lorem-move.patch &&
+	test_path_is_dir .git/rebase-apply &&
+	test_cmp_rev lorem2^^ HEAD &&
+
+	test_must_fail git am <lorem-move.patch &&
+	test_path_is_dir .git/rebase-apply &&
+	test_cmp_rev lorem2^^ HEAD
+'
+
 test_expect_success 'am --resolved works' '
 	echo goodbye >expected &&
 	rm -fr .git/rebase-apply &&