Java，单元测试模拟 mxbean

Question

我想在 CPU 时间对所有 Java 线程进行排序。我使用 ThreadMXBean 通过线程 ID 获取线程的 CPU 时间。比较器用于对线程 ID 进行排序。

public class ThreadStats{
    private static ThreadMXBean mxbean = ManagementFactory.getThreadMXBean();

    class ThreadCPUCompare implements Comparator<Long>{

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

并且我进行了以下单元测试：

@RunWith(MockitoJUnitRunner.class)
public class ThreadStatsTest {

@InjectMocks ThreadCPUCompare comperator = new ThreadStats().new ThreadCPUCompare();
@Mock ThreadMXBean mxbean;

@Test
public void threadCPUSortTest() {
    Mockito.when(mxbean.getThreadCpuTime(1L)).thenReturn(3L);
    Mockito.when(mxbean.getThreadCpuTime(2L)).thenReturn(2L);
    Mockito.when(mxbean.getThreadCpuTime(3L)).thenReturn(4L);
    Mockito.when(mxbean.getThreadCpuTime(4L)).thenReturn(1L);

    List<Long>expectedList = new ArrayList<Long>();
    expectedList.add(3L);
    expectedList.add(1L);
    expectedList.add(2L);
    expectedList.add(4L);

    List<Long>actualList = new ArrayList<Long>();
    actualList.add(4L);
    actualList.add(2L);
    actualList.add(3L);
    actualList.add(1L);


    //Sorting of the actual list
    Collections.sort(actualList, comperator);

    assertEquals(expectedList, actualList);
    }
}

但我无法让测试正常工作。我认为是因为嘲笑不起作用。有人可以告诉我如何修复单元测试吗？

Answer 1

您的测试失败，因为没有注入模拟。 Mockito 不会注入静态字段，也不会注入外部 class（例如您的 ThreadStats class）。

你需要这样写代码：

class ThreadCPUCompare implements Comparator<Long>
{
    private ThreadMXBean mxbean;

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

@RunWith(MockitoJUnitRunner.class)
public class ThreadStatsTest
{
    @Mock ThreadMXBean mxbean;
    @InjectMocks Comparator comperator = new ThreadCPUCompare();

    @Test
    public void threadCPUSortTest() {
        // do your tests exactly as before
    }
}

然后您将面临将其连接到生产代码中的挑战，但这是一个不同的练习，我会推荐某种依赖注入（guice、spring、手册等，具体取决于上下文和首选项）。

Answer 2

编写测试的一种简单方法如下，不涉及模拟：

public class ThreadStatsTest {
    Comparator<Long> comparator = new ThreadStats().new ThreadCPUCompare();

    @Test
    public void orderThreadIdsFromLongestToShortestCPUTime() {
        long longLivedThread = Thread.currentThread().getId(); // > 0 cpu time
        long shortLivedThread = new Thread().getId(); // 0 cpu time

        int longTimeFirst = comparator.compare(longLivedThread, shortLivedThread);
        int sameTimes = comparator.compare(longLivedThread, longLivedThread);
        int longTimeSecond = comparator.compare(shortLivedThread, longLivedThread);

        assertEquals(-1, longTimeFirst);
        assertEquals( 0, sameTimes);
        assertEquals( 1, longTimeSecond);
    }
}

Java，单元测试模拟 mxbean

Java, unit test mocking mxbean

java

unit-testing

mocking

mxbean