anchor.diff:        _kBranch,
         'origin/$_kBranch',
       ], workingDirectory: testDirectory.path, trace: true);
  +    expect(exitCode, 0);
   
       // Step 3. Revert to a prior version.
  -    await processUtils.stream(<String>[
  +    exitCode = await processUtils.stream(<String>[
         'git',
         'reset',
         '--hard',
         _kInitialVersion,
       ], workingDirectory: testDirectory.path, trace: true);
  +    expect(exitCode, 0);
   
       // Step 4. Upgrade to the newest dev. This should update the persistent
       // tool state with the sha for v1.14.3
  -    await processUtils.stream(<String>[
  +    exitCode = await processUtils.stream(<String>[
         flutterBin,
         'upgrade',
  +      '--verbose',
         '--working-directory=${testDirectory.path}'
       ], workingDirectory: testDirectory.path, trace: true);
  +    expect(exitCode, 0);
   
       // Step 5. Verify that the version is different.
       final RunResult versionResult = await processUtils.run(<String>[
  
positive.code:     final Directory testDirectory = parentDirectory.childDirectory('flutter');
      testDirectory.createSync(recursive: true);
  
      // Enable longpaths for windows integration test.
      await processManager.run(<String>[
        'git', 'config', '--system', 'core.longpaths', 'true',
      ]);
  
      // Step 1. Clone the dev branch of flutter into the test directory.
      await processUtils.stream(<String>[
        'git',
        'clone',
        'https://github.com/flutter/flutter.git',
      ], workingDirectory: parentDirectory.path, trace: true);
  
      // Step 2. Switch to the dev branch.
      await processUtils.stream(<String>[
        'git',
        'checkout',
        '--track',
  
negative.code:     expect(versionResult.stdout, isNot(contains(_kInitialVersion)));
  
      // Step 6. Downgrade back to initial version.
      exitCode = await processUtils.stream(<String>[
         flutterBin,
        'downgrade',
        '--no-prompt',
        '--working-directory=${testDirectory.path}'
      ], workingDirectory: testDirectory.path, trace: true);
      expect(exitCode, 0);
  
      // Step 7. Verify downgraded version matches original version.
      final RunResult oldVersionResult = await processUtils.run(<String>[
  