Android Test: ClassCastException: org.mockito.Answers cannot be cast to org.mockito.stubbing.Answer

[cypressious]

I'm getting the following exception when I try to run a test that previously worked without mockito-kotlin:

java.lang.ClassCastException: org.mockito.Answers cannot be cast to org.mockito.stubbing.Answer
at com.nhaarman.mockito_kotlin.CreateInstanceKt.uncheckedMock(CreateInstance.kt:178)
at com.nhaarman.mockito_kotlin.CreateInstanceKt.createInstance(CreateInstance.kt:58)

I'm trying to isolate the code that is causing it.

Using version 0.5

[nhaarman]

Could this have something to do with #35?

[cypressious]

Here's a test case to reproduce it:

class KotlinMockitoTest {
    @Test
    fun test() {
        val mock = mock<Func1<String, String>>()
        whenever(mock.call(any())).thenReturn("foo")
        assertEquals("foo", mock.call("bar"))
    }
}

Func1 is any Java interface, like the one from RxJava.

Since the test is run as an android instrumentation test, I should mention that I had to force an older mockito dependency, because mockito 2.0 doesn't work with dexmaker. My dependencies are declared as follows.

androidTestCompile 'org.mockito:mockito-core:1.9.5'
androidTestCompile('com.nhaarman:mockito-kotlin:0.5.0') {
    exclude group: 'org.jetbrains.kotlin'
    exclude group: 'org.mockito'
}
androidTestCompile 'com.google.dexmaker:dexmaker:1.2'
androidTestCompile 'com.google.dexmaker:dexmaker-mockito:1.2'

[AdrianAtHumboldt]

I believe the older Mockito version is the cause: I also had this issue in a (non-Android) project using an older Mockito version, and resolved by upgrading to Mockito 2.0.

[pvorb]

I use Mockito 1.10.19 since Mockito 2 is still in beta and also face this issue.

Maybe I can find a way to achieve the same functionality in a way compatible to both Mockito 1 and 2 and come up with a patch.

[pvorb]

I ended up with something like this

@Suppress("UNCHECKED_CAST")
private fun <T> Class<T>.uncheckedMock(): T {
    // use fallback for pre 2.0 Mockito versions
    val defaultAnswer: Answer<*> =
            if (Answers.RETURNS_DEFAULTS is Answer<*>)
                Answers.RETURNS_DEFAULTS
            else
                GloballyConfiguredAnswer()

    val impl = MockSettingsImpl<T>().defaultAnswer(defaultAnswer) as MockSettingsImpl<T>
    val creationSettings = impl.confirm(this)
    return MockUtil().createMock(creationSettings).apply {
        if (this is Any && this.javaClass.simpleName == "MockAccess") {
            (this as MockMethodInterceptor.MockAccess).mockitoInterceptor = null
        }
    }
}

But unfortunately suddenly I was unable to reproduce the ClassCastException when reverting back to the version without this change, even with your test case from above.

@cypressious Could you check if the above code snippet works for you?

[nhaarman]

If anyone could make a PR with a solid test that fails with this issue, we could try and tackle it.

[zeitlinger]

I can confirm that this problem exists before Mockito 2.

This is the test case that I used to check

    @Test
    fun verifyTest() {
        open class Klass {
            open fun doIt(list: List<String>) {

            }
        }

        val klass: Klass = mock()

        val c: ArgumentCaptor<List<String>> = argumentCaptor()

        klass.doIt(ArrayList())

        verify(klass).doIt(capture(c))
    }

[nhaarman]

It looks like this issue and #35 are caused by using Mockito 1.x. This library really focuses on the soon-to-be-released 2.x version.

[nimloth05]

I believe the randomness of this problem stems from classloaders loading multiple versions of mockito. I had the same problem even after upgrading kotlin_mockito to 0.11. Juckito, another support library for mockito, uses version 1.x of Mockito.

Move the juckito declaration or any other library which pulls in Mockito 1.x to the end of the include list. I add this comment, because google led me here (first hit of my search)