How to use MockCreationValidatorTest class of org.mockito.internal.util package

I had a test dependency on a third-party jar which used powermock. In order to resolve this error, I had to add:

@PowerMockIgnore("jdk.internal.reflect.*")

To the class that is tested with powermock

What do you need most:

1. The ability to make sure that somebody doesn't inherit from your class, OR
2. The ability to make sure that your code is testable using your mocking framework of choice?

Generally, I believe that you don't need to enforce (1). For me, testability (2), is far more important. What fits your situation best?

JUnit 5 has @TestInstance(PER_CLASS) annotation that can be used for this purpose. One of the features that it enables is non-static BeforeAll and AfterAll methods:

@TestInstance(PER_CLASS)
class BeforeAllTests {

    lateinit var isInit = false

    @BeforeAll
    fun setup() {
        isInit = true
    }

   @TestFactory
   fun beforeAll() = listOf(
       should("initialize isInit in BeforeAll") {
           assertTrue(isInit)
       }
   )
}

fun should(name: String, test: () -> Unit) = DynamicTest.dynamicTest("should $name", test)

In new Mockito versions you can use stubbing consecutive calls to throw exception on first can and returning a value on a second call.

when(mock.someMethod("some arg"))
    .thenThrow(new RuntimeException())
    .thenReturn("foo");

https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#10

You can write your own Answer:

when(mock.testMethod(anyString())).thenAnswer(new Answer<String>() {
    @Override
    public String answer(InvocationOnMock invocation) {
        return invocation.getArgumentAt(0, String.class);
    }
});

Or:

when(mock.testMethod(anyString()))
    .thenAnswer(AdditionalAnswers.<String>returnsFirstArg());

Another way of dealing with this issue is the following:

/**
 * This method overcomes the issue with the original Mockito.spy when passing a lambda which fails with an error
 * saying that the passed class is final.
 */
@SuppressWarnings("unchecked")
static <T, P extends T> P spyLambda(Class<T> lambdaType, P lambda) {
    return (P) mock(lambdaType, delegatesTo(lambda));
}

Which allows spying the lambda by changing the first method as following:

@Test
void spyingLambda() {
    Supplier<String> spy = spyLambda(Supplier.class, () -> "1");
    spy.get();
}

Hopefully the above examples might help others who encounter the same issue.

Take a look at this reference in the official API. You want to reverse the way your call is made and adjust the argument too, since this is a void method that you expect to throw an exception.

doThrow(new ContentIOException()).when(StubbedObject).putContent(contentStream);

@Mock creates a mock. @InjectMocks creates an instance of the class and injects the mocks that are created with the @Mock (or @Spy) annotations into this instance.

Note you must use @RunWith(MockitoJUnitRunner.class) or Mockito.initMocks(this) to initialize these mocks and inject them (JUnit 4).

With JUnit 5, you must use @ExtendWith(MockitoExtension.class).

@RunWith(MockitoJUnitRunner.class) // JUnit 4
// @ExtendWith(MockitoExtension.class) for JUnit 5
public class SomeManagerTest {

    @InjectMocks
    private SomeManager someManager;

    @Mock
    private SomeDependency someDependency; // this will be injected into someManager
 
     // tests...

}

OK, this is a bad thing to be doing. Don't mock a list; instead, mock the individual objects inside the list. See Mockito: mocking an arraylist that will be looped in a for loop for how to do this.

Also, why are you using PowerMock? You don't seem to be doing anything that requires PowerMock.

But the real cause of your problem is that you are using when on two different objects, before you complete the stubbing. When you call when, and provide the method call that you are trying to stub, then the very next thing you do in either Mockito OR PowerMock is to specify what happens when that method is called - that is, to do the thenReturn part. Each call to when must be followed by one and only one call to thenReturn, before you do any more calls to when. You made two calls to when without calling thenReturn - that's your error.