anchor.diff:      });
   
       testWithoutContext('handles a null parent', () {
  -      final _Device device = _Device();
  +      final FakeDevice device = FakeDevice();
   
         expect(() => eventPrinter.handleFinishedTest(device), returnsNormally);
         expect(() => eventPrinter.handleStartedDevice(observatoryUri), returnsNormally);
  
positive.code:   });
  }
  
  class _Device extends Mock implements TestDevice {}
  
negative.code: 
  import 'package:flutter_tools/src/test/event_printer.dart';
  import 'package:flutter_tools/src/test/test_device.dart';
  import 'package:test/fake.dart';
  
  import '../../src/common.dart';
  
  