Fix Dart Tests

Author: PineappleIOnic

templates/dart/test/id_test.dart.twig

@@ -7,8 +7,8 @@ import 'package:flutter_test/flutter_test.dart';
 
 void main() {
   group('unique()', () {
-    test('returns unique()', () {
-      expect(ID.unique(), 'unique()');
+    test('returns unique ID', () {
+      expect((ID.unique()).length, 20);
     });
   });