@Override
    public Comparator<? super E> comparator() {
        return underlying().comparator();
    }
@Test
    public void testDelegationOfComparator() {
        TreePSet<Integer> testSet = TreePSet.from(Arrays.asList(3, 4, 5));
        new PCollectionsTreeSetWrapperDelegationChecker<>()
                .defineMockConfigurationForFunctionInvocation(TreePSet::comparator, testSet.comparator())
                .defineWrapperFunctionInvocationAndMockReturnValueTransformation(PCollectionsImmutableNavigableSet::comparator, identity())
                .doFunctionDelegationCheck();
    }