t5521: test --dry-run does not make any changes

Test that when --dry-run is provided to git-pull, it does not make any
changes, namely:

* --dry-run gets passed to git-fetch, so no FETCH_HEAD will be created
  and no refs will be fetched.

* The index and work tree will not be modified.

Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5521-pull-options.sh

@@ -117,4 +117,17 @@ test_expect_success 'git pull --all' '
 	)
 '
 
+test_expect_success 'git pull --dry-run' '
+	test_when_finished "rm -rf clonedry" &&
+	git init clonedry &&
+	(
+		cd clonedry &&
+		git pull --dry-run ../parent &&
+		test_path_is_missing .git/FETCH_HEAD &&
+		test_path_is_missing .git/refs/heads/master &&
+		test_path_is_missing .git/index &&
+		test_path_is_missing file
+	)
+'
+
 test_done