Vararg method call on mock object fails when used org.mockito.AdditionalAnswers#delegatesTo

I try to mock interface with varargs method and default implementation in final class and get this error:

java.lang.IllegalArgumentException: wrong number of arguments

    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:498)
    at org.mockito.internal.stubbing.defaultanswers.ForwardsInvocations.answer(ForwardsInvocations.java:31)
    at org.mockito.internal.handler.MockHandlerImpl.handle(MockHandlerImpl.java:93)
    at org.mockito.internal.handler.NullResultGuardian.handle(NullResultGuardian.java:29)
    at org.mockito.internal.handler.InvocationNotifierHandler.handle(InvocationNotifierHandler.java:38)
    at org.mockito.internal.creation.MethodInterceptorFilter.intercept(MethodInterceptorFilter.java:51)

I run the following code:

public class DefaultAnswerDemo {

    public interface Foo {
        void bar(String baz, Object... args);
    }

    public static final class FooImpl implements Foo {

        @Override
        public void bar(String baz, Object... args) {
            System.out.println("bar");
        }

    }

    @Test
    public void defaultAnswerTest() {
        Foo fooImpl = new FooImpl();

        Foo foo = mock(Foo.class, withSettings()
                .defaultAnswer(delegatesTo(fooImpl)));

        foo.bar("baz", 12, "45", 67.8);
    }

}

This is happens because org.mockito.internal.invocation.InvocationImpl by default expands varargs arguments to flat list. And I have no idea, how correctly fix this.

[ChristianSchwarz]

Adding new API or changing existing behaviour need to be discussed with the core-members.

I agree with you, getArguments() should return unaltered/not expanded arguments. The current getArguments() implementation has also the problem that is can’t distinguish an null-vararg argument / varArgMethod(new Type[]{null}) from an null-varag array / varArgMethod((Type[])null).

[andreymanzharov]

Yes, I agree with you. But I think, this is already a bit confusing that method getArgument() returns expanded varargs. Maybe we need two methods getArguments() and getExpandedArguments()?