Cast exception when mocking kotlin lambda callbacks in Mockk

问题

I am having some trouble mocking callback functions with Mockk.

I am trying to mock a task success listener that is called like this:

collection
    .add(Item())
    .addOnSuccessListener {
        update(collection.document(it.id))
    }

Where the java signature for the callback would look like this:

public interface OnSuccessListener<T> {
    void onSuccess(T var1);
}

and the signature for addOnSuccessListener looks like this

public abstract Task<DocumentReference> addOnSuccessListener(@NonNull OnSuccessListener<DocumentReference> var1);

My mock looks like this:

every { documentReferenceTask.addOnSuccessListener(any()) } answers {
    firstArg<(DocumentReference) -> Unit>().onSuccess(documentReference)
    value
}

I have also tried:

every { documentReferenceTask.addOnSuccessListener(any()) } answers {
    firstArg<OnSuccessListener<DocumentReference>>().invoke(documentReference)
    value
}

Either way, I am receiving a cast exception like:

java.lang.ClassCastException: com.package.MyClass$addProduct$1 cannot be cast to kotlin.jvm.functions.Function1

回答1:

Oops, I was misreading the error.

every { documentReferenceTask.addOnSuccessListener(any()) } answers {
    firstArg<OnSuccessListener<DocumentReference>>().invoke(documentReference)
    value
}

This method works, the cast exception was from the second line. The correction looks like

every { documentReferenceTask.addOnSuccessListener(any()) } answers {
    firstArg<OnSuccessListener<DocumentReference>>().invoke(documentReference)
    **documentReferenceTask**
}

来源：https://stackoverflow.com/questions/53808565/cast-exception-when-mocking-kotlin-lambda-callbacks-in-mockk

标签

unit-testing

kotlin

mockk