anchor.diff:    void createSync(String target, {bool recursive: false}) {}
     void updateSync(String target) {}
     Future<Link> update(String target) => null;
  +  Future<bool> exists() => null;
  +  bool existsSync() => false;
     Future<String> resolveSymbolicLinks() => null;
     String resolveSymbolicLinksSync() => null;
     Future<Link> rename(String newPath) => null;
  
positive.code:   File renameSync(String newPath) => null;
    Future<File> copy(String newPath) => null;
    File copySync(String newPath) => null;
    Future<int> length() => null;
    int lengthSync() => null;
    File get absolute => null;
  
negative.code: }
  
  class LinkMock extends FileSystemEntity implements Link {
    String get path => "/mocklink";
  
    LinkMock(String path);
  
    static createLink(String path) => new LinkMock(path);
  