anchor.diff:      });
     });
   }
  +
  +class MockArtifacts extends Mock implements Artifacts {}
  +class MockKernelCompiler extends Mock implements KernelCompiler {}
  
positive.code:               .codeUnits
          ]));
  
          final LaunchResult result = await device.startApp(null,
              mainPath: mainPath,
              debuggingOptions: new DebuggingOptions.enabled(
                  const BuildInfo(BuildMode.debug, null)));
          expect(result.started, isTrue);
          expect(result.observatoryUri, observatoryUri);
  
  
negative.code:           await device.startApp(null,
                mainPath: mainPath,
                debuggingOptions: new DebuggingOptions.disabled(
                    const BuildInfo(BuildMode.debug, null, previewDart2: true)));
          }, throwsToolExit());
        }, overrides: startOverrides);
  
  