t4151: am --abort will keep dirty index intact

Since 7b3b7e3 (am --abort: keep unrelated commits since the last failure
and warn, 2010-12-21), git-am --abort will not touch the index if on the
previous invocation, git-am failed because the index is dirty. This is
to ensure that the user's modifications to the index are not discarded.

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/t4151-am-abort.sh

@@ -95,6 +95,21 @@ test_expect_success 'am --abort will keep the local commits intact' '
 	test_cmp expect actual
 '
 
+test_expect_success 'am --abort will keep dirty index intact' '
+	git reset --hard initial &&
+	echo dirtyfile >dirtyfile &&
+	cp dirtyfile dirtyfile.expected &&
+	git add dirtyfile &&
+	test_must_fail git am 0001-*.patch &&
+	test_cmp_rev initial HEAD &&
+	test_path_is_file dirtyfile &&
+	test_cmp dirtyfile.expected dirtyfile &&
+	git am --abort &&
+	test_cmp_rev initial HEAD &&
+	test_path_is_file dirtyfile &&
+	test_cmp dirtyfile.expected dirtyfile
+'
+
 test_expect_success 'am -3 stops on conflict on unborn branch' '
 	git checkout -f --orphan orphan &&
 	git reset &&