anchor.diff:      return _tasks.containsKey(taskName);
     }
   
  -  Task _getTask(String taskName) {
  -    return _tasks[taskName];
  -  }
  -
     void addSync(String name, Func1<TaskContext, bool> func) {
       addTask(name, new Task.sync(func));
     }
  
positive.code:     }
    }
  
    void _addHelpTask(String helpTaskName) {
      assert(_helpTaskName == null);
      addTask(helpTaskName, _getHelpTask());
      _helpTaskName = helpTaskName;
    }
  
    void freeze() {
      require(!isFrozen, "Already frozen.");
      final list = new List<String>.from(_tasks.keys);
  
negative.code:   void doPrint(Object value) {
      print(value);
    }
  
    void _addHelpTask(String helpTaskName) {
      assert(_helpTaskName == null);
      addTask(helpTaskName, _getHelpTask());
      _helpTaskName = helpTaskName;
    }
  
    Task _getTask(String taskName) {
      return _tasks[taskName];
    }
  }
  