Mockito.mockStatic not working with Kotlin but it works in Java

[aakash1313]

I was trying a mock a static method inside my Kotlin class for a unit test, but it seems the Java version of my Unit Test is successful but the Kotlin version is failing

@RunWith(RobolectricTestRunner.class)
public class MyTest {

    @Test
    public void givenStaticMethodWithArgs_whenMocked_thenReturnsMockSuccessfully() {
        RestAdapterFactory restAdapterFactoryMock = Mockito.mock(RestAdapterFactory.class);
        try (MockedStatic<RestAdapterFactory> utilities = Mockito.mockStatic(RestAdapterFactory.class)) {
            utilities.when(() -> RestAdapterFactory.getInstance(Mockito.any()))
                    .thenReturn(restAdapterFactoryMock);

            assertEquals(restAdapterFactoryMock, RestAdapterFactory.getInstance("fd"));
        }
    }
}

This test is running successfully but the Kotlin version of it below is failing

Kotlin Version

@Test
fun givenStaticMethodWithArgs_whenMocked_thenReturnsMockSuccessfully() {
val restAdapterFactoryMock = Mockito.mock(RestAdapterFactory::class.java)
Mockito.mockStatic(RestAdapterFactory::class.java).use { utilities ->
utilities.`when`<Any> { getInstance(Mockito.any()) }.thenReturn(restAdapterFactoryMock)
Assert.assertEquals(restAdapterFactoryMock, getInstance("test"))
  }
} 

Getting the below exception:

You cannot use argument matchers outside of verification or stubbing.
Examples of correct usage of argument matchers:
    when(mock.get(anyInt())).thenReturn(null);
    doThrow(new RuntimeException()).when(mock).someVoidMethod(any());
    verify(mock).someMethod(contains("foo"))

Can someone help with this ?

[navinpd]

Basically when we write code in kotlin the java bytecode conversion creates multiple layer of static, final classes & functions. This makes the mocking difficult on multiple layers of static / final functions. Easy for investigation is to look for decompiled bytecode.