anchor.diff:  class A {} // 1
   class B = Object with A; // 2
   ''');
  -    ClassElement elementA = findElement('A');
  +    ClassElement elementA = findElement.class_('A');
       assertThat(elementA).isMixedInAt('A; // 2', false);
     }
   
  
positive.code:     print(method); // nq
    }
  }''');
      MethodElement element = findElement('method');
      assertThat(element)
        ..isReferencedAt('method); // q', true)
        ..isReferencedAt('method); // nq', false);
  
negative.code:   A.bar();
  }
  ''');
      var constA = findElement.unnamedConstructor('A');
      var constA_bar = findElement.constructor('bar');
      assertThat(constA).isReferencedAt('(); // 2', true, length: 0);
      assertThat(constA_bar).isReferencedAt('.bar(); // 1', true, length: 4);
    }
  