某任务如果被多个模块引用，可以把它定义为一个独立的模块（只包括该任务），并可 用层次命名来引用它。这个例子说明如何在测试模块中运用任务。-If a task is referenced by a number of modules, it can be defined as an independent module (including the task), and can be used to refer to it as a hierarchy. This example shows