使用PowerMock写单元测试，mock方法调用失败

Question

我最近学习使用 PowerMock 为名为 Module 的 class 编写单元测试，它扩展了 class Base。他们看起来像这样。

public class Base {
    protected final static ServiceA serviceA;
    protected final static ServiceB serviceB;
    static {
        serviceA = ServiceA.getInstance();
        serviceB = ServiceB.getInstance();
    }
}

public class Module extends Base {
    public DataA methodA() {
        return serviceA.getDataA();
    }
    public DataB methodB() {
        return serviceB.getDataB();
    }
}

我的单元测试是这样的：

@PowerMockIgnore("javax.management.*")
@RunWith(PowerMockRunner.class)
@PrepareForTest({Module.class, ServiceA.class, ServiceB.class})
public class ModuleTest {
    private Module module;
    @Mock
    private ServiceA serviceA;
    @Mock
    private ServiceB serviceB;

    @Before
    public void setup() throws Exception {
        MockitoAnnotations.initMocks(this);

        PowerMockito.mockStatic(ServiceA.class);
        PowerMockito.when(ServiceA.getInstance).thenReturn(serviceA);

        PowerMockito.mockStatic(ServiceB.class);
        PowerMockito.when(ServiceB.getInstance).thenReturn(serviceB);

        module = new Module();
        // I spy it because it has other methods I need to mock
        module = PowerMockito.spy(module);
    }

    @Test
    public void methodATest() {
        DataA dataA = new DataA();
        PowerMockito.when(serviceA.getDataA()).thenReturn(dataA);
        DataA data = module.methodA();
        assertEquals(dataA, data);
    }
    @Test
    public void methodBTest() {
        DataB dataB = new DataB();
        PowerMockito.when(serviceB.getDataB()).thenReturn(dataB);
        DataB data = module.methodB();
        assertEquals(dataB, data);
    }
}

一切看起来都很简单，但是当我运行 ModuleTest 时， methodBTest() 没有通过。似乎 PowerMockito.when(serviceB.getDataB()).thenReturn(dataB) 不起作用并调用真正的 serviceB.getDataB() 方法。所以 assertEquals(dataB, data) 抛出 org.junit.ComparisonFailure.

如果我将 methodBTest() 放在 methodATest() 之前，methodATest() 不会通过。同样的原因。

如果我将 PowerMockito.when(serviceA.getDataA()).thenReturn(dataA) 和 PowerMockito.when(serviceB.getDataB()).thenReturn(dataB) 放在 setup() 中，一切都会完美无缺。

这整天都让我很困扰。有谁知道为什么会这样以及如何解决？我需要在各自的测试方法中编写模拟语句，因为我可能会更改返回值。

Answer 1

这是一个（几乎）没有变化的解决方案

@PowerMockIgnore("javax.management.*")
@RunWith(PowerMockRunner.class)
@PrepareForTest({Module.class, ServiceA.class, ServiceB.class})
public class ModuleTest {
    private Module module;

    private static ServiceA serviceA = Mockito.mock(ServiceA.class);

    private static ServiceB serviceB = Mockito.mock(ServiceB.class);

    @BeforeClass
    public static void oneTimeSetup() throws Exception {
        PowerMockito.mockStatic(ServiceA.class);
        PowerMockito.when(ServiceA.class, "getInstance").thenReturn(serviceA);

        PowerMockito.mockStatic(ServiceB.class);
        PowerMockito.when(ServiceB.class, "getInstance").thenReturn(serviceB);
    }

    @Before
    public void setup() throws Exception {
        module = new Module();
        // I spy it because it has other methods I need to mock
        module = PowerMockito.spy(module);
    }

    @Test
    public void methodATest() {
        DataA dataA = new DataA();
        Mockito.when(serviceA.getDataA()).thenReturn(dataA);
        DataA data = module.methodA();
        assertEquals(dataA, data);
    }
    @Test
    public void methodBTest() {
        DataB dataB = new DataB();
        Mockito.when(serviceB.getDataB()).thenReturn(dataB);
        DataB data = module.methodB();
        assertEquals(dataB, data);
    }
}

更改了什么（以及为什么）：

在Base中：serviceA和serviceB改为protected（Module私有则不能访问）
使用 "proper" (AFAIK) 语法 PowerMockito.when(ServiceA.class, "getInstance").thenReturn(serviceA);
使用 @BeforeClass 并在 Base

serviceA

serviceB

使用 Junit 4.12、PowerMockito 1.6.2 进行测试。

注意：也可以利用 @SuppressStaticInitializationFor 来实现相同的目标：

@SuppressStaticInitializationFor(value = "so46196071.Base") // suppress the static in Base (note this is my package name)
@PowerMockIgnore("javax.management.*")
@RunWith(PowerMockRunner.class)
@PrepareForTest({Module.class, ServiceA.class, ServiceB.class})
public class ModuleBisTest {
    private Module module;

    @Mock
    private ServiceA serviceA;

    @Mock
    private ServiceB serviceB;

    @Before
    public void setup() throws Exception {
        // MockitoAnnotations.initMocks(this); /* this is not needed => done by the runner */

        PowerMockito.mockStatic(ServiceA.class);
        PowerMockito.when(ServiceA.class, "getInstance").thenReturn(serviceA);

        PowerMockito.mockStatic(ServiceB.class);
        PowerMockito.when(ServiceB.class, "getInstance").thenReturn(serviceB);

        module = new Module();
        Whitebox.setInternalState(Base.class, "serviceA", serviceA); // set serviceA in Base "by hand"
        Whitebox.setInternalState(Base.class, "serviceB", serviceB); // set serviceB in Base "by hand"
        // I spy it because it has other methods I need to mock
        module = PowerMockito.spy(module);
    }

    // ...

使用PowerMock写单元测试，mock方法调用失败

Using PowerMock to write unit test, mocked method fails to invoke

java

junit

unit-testing

mockito

powermock