fix up tests

test/list_path_observer_test.dart

Index: test/list_path_observer_test.dart
diff --git a/test/list_path_observer_test.dart b/test/list_path_observer_test.dart
index 3010d128305efbb4d5c8ae4a41cef11cf03a54e5..eddaf8cbea6fae0aee51735e08afbf141823a757 100644
--- a/test/list_path_observer_test.dart
+++ b/test/list_path_observer_test.dart
@@ -7,7 +7,13 @@ import 'package:observe/observe.dart';
 import 'package:unittest/unittest.dart';
 import 'observe_test_utils.dart';
 
-main() => dirtyCheckZone().run(_runTests);
+import 'package:observe/mirrors_used.dart'; // make test smaller.
+import 'package:smoke/mirrors.dart';
+
+main() {
+  useMirrors();
+  dirtyCheckZone().run(_runTests);
+}
 
 _runTests() {
   var list;