使用模拟对方法进行单元测试

Question

我想对此方法进行单元测试。我知道我需要嘲笑 mxbean，但我不知道该怎么做。有人可以告诉我如何对此方法进行单元测试吗？

@Override
public int compare(Long threadId1, Long threadId2) {
    ThreadMXBean mxbean = ManagementFactory.getThreadMXBean();
    return Long.compare(mxbean.getThreadCpuTime(threadId2), mxbean.getThreadCpuTime(threadId1));
}

Answer 1

事实上，它不能有效地被嘲笑。您需要将局部变量移动到字段。

ThreadMXBean mxbean = ManagementFactory.getThreadMXBean();
@Override
public int compare(Long threadId1, Long threadId2) {
    return Long.compare(mxbean.getThreadCpuTime(threadId2), mxbean.getThreadCpuTime(threadId1));
}

现在，您可以在测试中将该字段重新分配给模拟（我将使用 Mockito，但也存在其他框架）：

@Test
public void yourTestMethod(){
    YourClass yourClass = new YourClass();
    ThreadMXBean mock = Mockito.mock(ThreadMXBean.class)
    Mockito.when(mxbean.getThreadCpuTime(1L)).thenReturn(1);
    Mockito.when(mxbean.getThreadCpuTime(2L)).thenReturn(2);
    yourClass.mxbean = mock;
    assertThat(yourClass.compare(1L, 2L), is(-1));
}

但是使用Mockito JUnit Runner并让Mockito自动创建模拟会更好：

@RunWith(MockitoJUnitRunner.class)
public class YourTest{
    @InjectMocks YourClass yourClass = new YourClass();
    @Mock ThreadMXBean mock;
    @Test
    public void yourTestMethodDoesntNeedToCreateMocksAnymore(){
        Mockito.when(mxbean.getThreadCpuTime(1L)).thenReturn(1);
        Mockito.when(mxbean.getThreadCpuTime(2L)).thenReturn(2);
        assertThat(yourClass.compare(1L, 2L), is(-1));
    }

}

最后：如果将所有 Mockito.* 调用替换为静态导入，测试将变得更可读，例如

MyFoo foo = mock(MyFoo.class);
when(foo.bar()).thenReturn(baz);