Why does Mockito expects my verification method to be called with `Nothing`?

Question

In my project I tried to setup a test in which should be verified that a method is called with a specific parameter. For this I am using Mockito and Kotlin.

In the test I am using a mock class. (publisher) This class is part of rosjava and contains a method publish;

public interface Publisher<T> extends TopicParticipant { //(java)
    void setLatchMode(boolean var1);

    boolean getLatchMode();

    T newMessage();

    void publish(T var1);

    boolean hasSubscribers();

    int getNumberOfSubscribers();

    void shutdown(long var1, TimeUnit var3);

    void shutdown();

    void addListener(PublisherListener<T> var1);
}

When I try to set my expectation like:

val publisherMock = mock(Publisher::class.java)

verify(publisherMock, atLeastOnce()).publish(message) // message is underlined with a red color

This does not compile and says that the parameter for publish should be of class Nothing!. Why is this?

do you have a class called Nothing which you use in this flow? — Stultuske, Jun 05 '19 at 13:43
No, I think it is referring to the Nothing class of Kotlin: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-nothing.html — Klyner, Jun 05 '19 at 13:45

score 2 · Accepted Answer · answered Jun 05 '19 at 14:13

That's because your Publisher class is generic. Creating mock with mock(Publisher::class.java) code creates Publisher<*> object (it means that type parameter is Nothing).

To solve it you can't just place type parameter in mock creating code - Publisher<String>::class.java is not a valid code for Java or Kotlin.

All you can do is unchecked cast:

val publisherMock = mock(Publisher::class.java) as Publisher<String>

If you need to disable warning from Android Studio just place @Suppress("UNCHECKED_CAST") line before that.

Why does Mockito expects my verification method to be called with `Nothing`?

1 Answers1