@Override
    public boolean add(E e) {
        // will throw UnsupportedOperationException
        return underlying().add(e);
    }
@Test
    public void testDelegationOfUnsupportedFunctionAdd() {
        new PCollectionsTreeSetWrapperDelegationChecker<>()
                .defineMockConfigurationForUnsupportedFunction(mock -> mock.add(eq(this)))
                .defineWrapperUnsupportedFunctionInvocation(wrapper -> wrapper.add(this))
                .doUnsupportedFunctionDelegationCheck();
    }