anchor.diff:  import 'package:spark_widgets/spark_menu_item/spark_menu_item.dart';
   import 'package:spark_widgets/spark_button/spark_button.dart';
   import 'package:spark_widgets/spark_modal/spark_modal.dart';
  +import 'package:spark_widgets/common/spark_widget.dart';
  +
   import 'package:unittest/unittest.dart';
   
   import '../../spark_polymer_ui.dart';
  
positive.code:     throw "Could not find button with title $title";
    }
  
    void clickButton(String title) => clickElement(getButton(title));
  }
  
  defineTests() {
  
negative.code:     return int.parse(opacity) > 0 && display != "none" && visibility == "visible";
    }
  
    List<SparkDialogButton> get dialogButtons =>
        dialog.querySelectorAll("spark-dialog-button");
  
    ModalUITester(this.id);
  
    SparkWidget getButtonByTitle(String title) {
      for (SparkWidget button in dialogButtons) {
        if (button.text.toLowerCase() == title.toLowerCase()) {
          return button;
        }
  