Stubbing a method that takes Class<T> as parameter with Mockito

There is a generic method that takes a class as parameter and I have problems stubbing it with Mockito. The method looks like this:

public <U extends Enum<U> & Error, T extends ServiceResponse<U>> T validate(
    Object target, Validator validator, Class<T> responseClass,
    Class<U> errorEnum);

It's god awful, at least to me... I could imagine living without it, but the rest of the code base happily uses it...

I was going to, in my unit test, stub this method to return a new empty object. But how do I do this with mockito? I tried:

).thenReturn(new UserCommentResponse());

but since I am mixing and matching matchers and raw values, I get "org.mockito.exceptions.misusing.InvalidUseOfMatchersException: Invalid use of argument matchers!"


The problem is, you cannot mix argument matchers and real arguments in a mocked call. So, rather do this:

).thenReturn(new UserCommentResponse());

Notice the use of the eq() argument matcher for matching equality.


Also, you could use the same() argument matcher for Class<?> types - this matches same identity, like the == Java operator.

Just in order to complete on the same thread, if someone want to stubb a method that takes a Class as argument, but don't care of the type, or need many type to be stubbed the same way, here is another solution:

private class AnyClassMatcher extends ArgumentMatcher<Class<?>> {

    public boolean matches(final Object argument) {
        // We always return true, because we want to acknowledge all class types
        return true;


private Class<?> anyClass() {
    return Mockito.argThat(new AnyClassMatcher());

and then call


Nice one @Ash. I used your generic class matcher to prepare below. This can be used if we want to prepare mock of a specific Type.(not instance)

private Class<StreamSource> streamSourceClass() {
    return Mockito.argThat(new ArgumentMatcher<Class<StreamSource>>() {

        public boolean matches(Object argument) {
            // TODO Auto-generated method stub
            return false;



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