anchor.diff:          outputPath: anyNamed('outputPath'),
           packagesFilePath: anyNamed('packagesFilePath'),
         )).thenAnswer((Invocation invocation) {
  -        globals.fs.file('example').createSync();
  +        fs.file('example').createSync();
           return Future<CompilerOutput>.value(CompilerOutput('example', 0, <Uri>[sourceFile.uri]));
         });
   
  
positive.code: 
  Future<File> _createPackage(FileSystem fs, String pkgName, String pkgFileName, { bool doubleSlash = false }) async {
    final Directory pkgTempDir = _newTempDir(fs);
    String pkgFilePath = globals.fs.path.join(pkgTempDir.path, pkgName, 'lib', pkgFileName);
    if (doubleSlash) {
      // Force two separators into the path.
      final String doubleSlash = globals.fs.path.separator + globals.fs.path.separator;
      pkgFilePath = pkgTempDir.path + doubleSlash + globals.fs.path.join(pkgName, 'lib', pkgFileName);
    }
    final File pkgFile = globals.fs.file(pkgFilePath);
    await pkgFile.parent.create(recursive: true);
    pkgFile.writeAsBytesSync(<int>[11, 12, 13]);
    _packages[pkgName] = globals.fs.path.toUri(pkgFile.parent.path);
    final StringBuffer sb = StringBuffer();
    _packages.forEach((String pkgName, Uri pkgUri) {
      sb.writeln('$pkgName:$pkgUri');
    });
    return globals.fs.file(globals.fs.path.join(_tempDirs[0].path, '.packages'))
      ..writeAsStringSync(sb.toString());
  }
  
  
negative.code:       expect(content.isModified, isFalse);
      });
      testUsingContext('file', () async {
        final File file = fs.file(filePath);
        final DevFSFileContent content = DevFSFileContent(file);
        expect(content.isModified, isFalse);
        expect(content.isModified, isFalse);
  