MissingMethodInvocationException testing an opened class in Kotlin - mockito

Question

I'm trying to make some integration tests with Kotlin + RxJava and MockWebServer. I'm kind of newbie in terms of testing and I'm Kotlin apprentice. I know about the limitations of Mockito and final classes, but I shouldn't be mocking the class I'm trying to test, so I don't know where is the real problem:
The error is the following:
Apr 16, 2016 9:59:49 PM okhttp3.mockwebserver.MockWebServer$3 execute
INFO: MockWebServer[54260] starting to accept connections
Apr 16, 2016 9:59:50 PM okhttp3.mockwebserver.MockWebServer$3 acceptConnections
INFO: MockWebServer[54260] done accepting connections: Socket closed
org.mockito.exceptions.misusing.MissingMethodInvocationException:
when() requires an argument which has to be 'a method call on a mock'.
For example:
when(mock.getArticles()).thenReturn(articles);
Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
Those methods *cannot* be stubbed/verified.
Mocking methods declared on non-public parent classes is not supported.
2. inside when() you don't call method on mock but on some other object.
at com.cesards.android.xxx.xxx.xxx.cloud.GoogleMapsApiClientShould.setUp(GoogleMapsApiClientShould.kt:34)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37)
at org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:234)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:74)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
And the class is the following:
#RunWith(MockitoJUnitRunner::class)
class GoogleMapsApiClientShould : MockWebServerShould() {
private lateinit var googleMapsApiClient: GoogleMapsApiClient
private val searchNearbyPlacesSubject: PublishSubject<List<GooglePlaceDTO>> = PublishSubject.create()
#Before override fun setUp() {
super.setUp()
val okHttpClient = GembasOkHttpClient()
val customApiClient = CustomApiClient(okHttpClient.okHttpClient, baseEndpoint)
googleMapsApiClient = GoogleMapsApiClient(customApiClient)
`when`(googleMapsApiClient.searchNearbyPlaces(LatLng(30.30, 30.30))).thenReturn(searchNearbyPlacesSubject)
}
#Test fun sendAcceptAndContentTypeHeaders() {
enqueueMockResponse()
searchNearbyPlacesSubject.onNext(listOf())
assertThatRequestContainsHeader("Accept", "application/json")
}
}
and
open class GoogleMapsApiClient(apiClient: CustomApiClient) : GoogleMapsApi
Any idea what is going on, guys? This is blowing my mind!!
PS: I know, for now I'm not mocking the dependencies after all, but I don't think it's related, right?