JUnit测试用例中的Thread.sleep [英] Thread.sleep in JUnit test case

问题描述

我正在编写一个测试用例来测试对象的行为。

I'm writing a test case to test an object behaviour.

当对象被实例化时，它必须允许调用方法，只允许调用call（）如果它在500毫秒内被调用，否则它必须抛出异常。

When the object is instantiated it must allow the call of a method let say call() only if it has been called within 500 ms, otherwise it must throw an exception.

我设计了这样的Junit测试用例：

I designed the Junit test case like this:

@Test(expected = IllegalStateException.class)
public void testCallAfterTimeout() {
    MyObject o= new MyObject();
    //To ensure the timeout is occurred
    Thread.sleep(1000);
    o.call();
}

您认为这是一种好习惯还是我应该采用其他方法？

Do you think is a good practice or I should follow another approach?

非常感谢

推荐答案

使用（实际）时间有两个问题在测试用例中：

There are two problems with using (real) time in test cases:

1. 这绝不是确定性的。特别是当您正在寻找高精度时，测试用例将在95％的时间内成功。但有时它们会失败，这些是最难调试的类型。请注意，在多线程测试用例中使用 Thread.sleep（）时，这更加困难。


2. 带睡眠的测试用例很长一段时间，这将使你的完整测试集运行繁琐。

1. It is never really deterministic. Especially when you are looking for high precision, testcases will succeed 95% of the time. But sometimes they fail, these are the hardest types of failure to debug. Note that when using Thread.sleep() with in a multithreaded test case this is even more difficult.
2. Test cases with sleeps take long to run, after a while this will make running your full testset cumbersome.

如果必须，你的方式是可以接受的。但还有其他选择：

If you must, your way is acceptable. But there are other options:

不要使用真正的时钟。而是使用可以从测试用例控制的假（模拟/存根）时钟：

Don't use a real clock. Instead use a fake (mocked/stubbed) clock that you can control from your testcase:

@Test(expected = IllegalStateException.class)
public void testCallAfterTimeout() {
    MyObject o= new MyObject();
    // Example function that you could make
    advanceClock(1000, TimeUnit.MILLISECONDS)
    o.call();
}

在您的对象中，您必须注入一个时钟。 MyObject 可能如下所示：

In your object you have to inject a clock. MyObject could look like this:

class MyObject
{

     public MyObject()
     {
           this(new Clock());
     }

     // Protected so only the test case can access it
     protected MyObject(Clock clock)
     {
           // Save clock as local variable, store creation time etc.
     }
} 

在Java 8中，一种机制为此提供了，例如参见 LocalDate.now（） 。但你也可以轻松实现自己的安静。

In Java 8 a mechanism for this is provided, see for instance LocalDate.now(). But you can also implement your own quiet easily.

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