anchor.diff:        PipelineWatcher(
           dir: libPath.absolute,
           pipeline: buildPipeline,
  +        // Ignore font files that are copied whenever tests run.
  +        ignore: (event) => event.path.endsWith('.ttf'),
         ).start();
         // Return a never-ending future.
         return Completer<bool>().future;
  
positive.code:   /// Used to watch a directory for any file system changes.
    final DirectoryWatcher watcher;
  
    void start() {
      watcher.events.listen(_onEvent);
    }
  
negative.code:   Timer _scheduledPipeline;
  
    void _onEvent(WatchEvent event) {
      if (ignore != null && ignore(event)) {
        return;
      }
  
      final String relativePath = path.relative(event.path, from: dir);
      print('- [${event.type}] ${relativePath}');
  
  