anchor.diff:  
     static void _testFalseIsFail() {
       final tasks = new Tasks();
  -    tasks.addTask('fail', _failedTask);
  +    tasks.addTask('fail', (ctx) => false);
       tasks.freeze();
   
       final runner = new Runner(tasks, ['fail']);
  
positive.code: 
    static void _testNullIsSad() {
      final tasks = new Tasks();
      tasks.addTask('null', _sadTask);
      tasks.freeze();
  
      final runner = new Runner(tasks, ['null']);
  
negative.code: 
      future.onComplete(onComplete);
    }
  }