anchor.diff:      expect(newElementA.name, 'aaa2');
       expect(elementB, isNotNull);
       expect(elementB.name, 'bbb');
  +    expect(helper.element.methods, [newElementA, elementB]);
       // verify delta
       expect(helper.delta.addedConstructors, isEmpty);
       expect(helper.delta.removedConstructors, isEmpty);
  
positive.code:     expect(elementA.name, 'A');
      expect(elementB.name, 'B');
      // unit.types
      expect(unitElement.types, unorderedEquals([elementA]));
      // verify delta
      expect(unitDelta.addedDeclarations, unorderedEquals([]));
      expect(unitDelta.removedDeclarations, unorderedEquals([elementB]));
  
negative.code:     expect(elementA.name, 'a');
      expect(elementB.name, 'b');
      // unit.types
      expect(
          unitElement.topLevelVariables, [elementA.variable, elementB.variable]);
      expect(unitElement.accessors, [elementA, elementB]);
    }
  
    test_unitMembers_class_add() {
  