UUID.getRandom 的 Powermock、mockStatic 在测试 class 中有效，但在 class 测试中无效

Question

奇怪的情况：使用 Powermock 模拟 UUID.getRandom()。这在 JUnit 测试 class 中有效，但是当被测试的 class（过滤器，如果重要的话）调用 UUID.getRandom 时，会生成一个唯一的 UUID。

简单测试用例

@RunWith(PowerMockRunner.class)
@PrepareForTest({UUID.class})
public class MyTest {

    private MyFilter filter;

    @Before
    public void setup() {

        //The most convenient way to get a UUID, have also tried creating one manually
        UUID uuid = UUID.randomUUID();

        mockStatic(UUID.class);

        PowerMockito.when(UUID.randomUUID()).thenReturn(uuid);

        filter = new MyFilter();
    }

    @Test
    public void testMyUUID() {

        //This test works
        assertEquals(UUID.randomUUID(), UUID.randomUUID());

    }

    @Test
    public void testFilterUUID() {

        //This test fails
        assertEquals(UUID.randomUUID(), filter.getUUID());
    }
}

简单class正在测试

public class MyFilter implements Filter {

    public UUID getUUID() {

        return UUID.randomUUID();
    }
}

很简单的东西，以前做过这样的模拟，只是想不通为什么这个案例不起作用。

使用 Powermock 1.5 版。

Answer 1

我相信 UUID 属于 "system classes" category, so you need to prepare for test the class calling UUID.randomUUID()(related github issue).，因此更改为 @PrepareForTest({MyFilter.class}) 应该可以解决问题。以下内容在 JUnit 4.4 和 Powermock 1.5 以及 JUnit 4.12 和 Powermock 1.7.3 中按预期工作：

@RunWith(PowerMockRunner.class)
@PrepareForTest(MyFilter.class)
public class MyTest {

    private MyFilter filter;

    @Before
    public void setup() {
        //The most convenient way to get a UUID, have also tried creating one manually
        UUID uuid = UUID.randomUUID();
        mockStatic(UUID.class);
        PowerMockito.when(UUID.randomUUID()).thenReturn(uuid);
        filter = new MyFilter();
    }

    @Test
    public void testMyUUID() {
        //This test works
        assertEquals(UUID.randomUUID(), UUID.randomUUID());

    }

    @Test
    public void testFilterUUID() {
        //This test fails
        assertEquals(UUID.randomUUID(), filter.getUUID());
    }
}

UUID.getRandom 的 Powermock、mockStatic 在测试 class 中有效，但在 class 测试中无效

Powermock, mockStatic of UUID.getRandom works in test class but doesn't in the class tested

uuid

powermock

mockstatic