@Override
    public PCollectionsImmutableNavigableSet<E> descendingSet() {
        return new PCollectionsImmutableNavigableSet<>(underlying().descendingSet());
    }
@Test
    public void testDelegationOfDescendingSet() {
        TreePSet<Integer> testSet = TreePSet.from(Arrays.asList(2, 3, 4));
        new PCollectionsTreeSetWrapperDelegationChecker<>()
                .defineMockConfigurationForFunctionInvocation(TreePSet::descendingSet, testSet.descendingSet())
                .defineWrapperFunctionInvocationAndMockReturnValueTransformation(PCollectionsImmutableNavigableSet::descendingSet, identity())
                .expectWrapperToWrapMockFunctionReturnValue()
                .doFunctionDelegationCheck();
    }