单元测试验证是否调用了伴生对象方法（模拟伴生对象）

当切换到 Kotlin 时，静态方法被移至伴生对象中。但是，没有明显的方法来对调用这些“静态方法”的其他方法进行单元测试。

在Java中，我们可以使用PowerMockito的MockStatic(SomeClass.class)来验证被测方法中是否调用了静态方法。 PowerMock 在 Kotlin 中失去了魔力。

为了进行测试，我创建了以下类。

public class DummyJava {
    static public Void staticMechod(){
          System.out.print("Dummy method is called");
          return null;
     }
}

class DummyCompanion {
    companion object {
        fun someCompanionMethod(){
            System.out.printf("companion method is called\n")
        }
    }
}

现在有另一个类称为DummyCompanion.someCompanion

public class DummyWrapper {
    public void callAStaticMethod(){
        DummyJava.staticMechod();
    }

    public void callCompanionMethod(){
        DummyCompanion.Companion.someCompanionMethod();
    }
}

进行单元测试callAStaticMethod()我们使用了以下内容

@RunWith(PowerMockRunner.class)
@PrepareForTest({DummyJava.class, DummyCompanion.Companion.class})
public class staticClassTest {
    //This case works
    @Test 
    public void testForStaticMethod() {
        PowerMockito.mockStatic(DummyJava.class);   
        DummyWrapper testObject = new DummyWrapper();

        Mockito.when(DummyJava.staticMechod()).thenCallRealMethod();

        testObject.callAStaticMethod();

        PowerMockito.verifyStatic(Dummy.class);
        DummyJava.staticMechod();
    }

    //This case doesn't work. It always passes.
    @Test
    public void testForCompanionMethod() {
        PowerMockito.mockStatic(DummyCompanion.Companion.class);
        DummyWrapper testObject = new DummyWrapper();
        testObject.callCompanionMethod();
PowerMockito.verifyStatic(DummyCompanion.Companion.class,Mockito.times(1));
        DummyCompanion.Companion.someCompanionMethod();
}

我的问题是如何验证调用了伴随方法。

解决方案1：在调用类中添加调用者函数

class DummyWrapper {
  val foo get() = DummyCompanion.Companion

  fun callAStaticMethod() {
    foo.staticMethod()
  }

  fun callCompanionMethod(){
    foo.someCompanionMethod();
  }
}

在测试类中，我们可以使用 Mockito 提供一个存根get()函数并验证它被调用。

@Test
fun testCase() {
  ....
  val mockCompanionObj: DummyCompanion.Companion = mock()
  val wrapper = DummyWrapper()

  whenever(wrapper.foo).thenReturn(mockCompanionObj)
  wrapper.callCompanionMethod()
  verify(mockCompanionObj).someCompanionMethod()
  ....
}

解决方案2：使用Mockk在 Mockk 中模拟伴随对象很容易。无需在源代码中插入测试接口对象。

@Test
fun testCompanionObject() {
  // Mock the companion object
  mockkObject(DummyCompanion.Companion)

  // Define the stubbing behavior of a companion object method
  every { DummyCompanion.someCompanionMethod() } answers { stubMethod() }

  val testObject = DummyWrapper()

  // Call a method that calls the companion object method
  // You can verify stubMethod() is called
  testObject.callCompanionMethod()

  verify(exactly = 1) { DummyCompanion.someCompanionMethod() }
}

详情请参阅Mockk https://mockk.io