t7610: add test case for rerere+mergetool+subdir bug

If rerere is enabled and mergetool is run from a subdirectory,
mergetool always prints "No files need merging".  Add an expected
failure test case for this situation.

Signed-off-by: Richard Hansen <hansenr@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7610-mergetool.sh

@@ -216,7 +216,7 @@ test_expect_success 'mergetool skips autoresolved' '
 	test "$output" = "No files need merging"
 '
 
-test_expect_success 'mergetool merges all from subdir' '
+test_expect_success 'mergetool merges all from subdir (rerere disabled)' '
 	test_when_finished "git reset --hard" &&
 	git checkout -b test$test_count branch1 &&
 	test_config rerere.enabled false &&
@@ -234,6 +234,25 @@ test_expect_success 'mergetool merges all from subdir' '
 	)
 '
 
+test_expect_failure 'mergetool merges all from subdir (rerere enabled)' '
+	test_when_finished "git reset --hard" &&
+	git checkout -b test$test_count branch1 &&
+	test_config rerere.enabled true &&
+	rm -rf .git/rr-cache &&
+	(
+		cd subdir &&
+		test_must_fail git merge master &&
+		( yes "r" | git mergetool ../submod ) &&
+		( yes "d" "d" | git mergetool --no-prompt ) &&
+		test "$(cat ../file1)" = "master updated" &&
+		test "$(cat ../file2)" = "master new" &&
+		test "$(cat file3)" = "master new sub" &&
+		( cd .. && git submodule update -N ) &&
+		test "$(cat ../submod/bar)" = "master submodule" &&
+		git commit -m "branch2 resolved by mergetool from subdir"
+	)
+'
+
 test_expect_success 'mergetool skips resolved paths when rerere is active' '
 	test_when_finished "git reset --hard" &&
 	test_config rerere.enabled true &&