@Override
    public ImmutableMap<K, V> removed(K key) {
        return new PCollectionsImmutableMap<>(underlying().minus(key));
    }
@Test
    public void testDelegationOfRemoved() {
        new PCollectionsHashMapWrapperDelegationChecker<>()
            .defineMockConfigurationForFunctionInvocation(mock -> mock.minus(eq(this)), SINGLETON_MAP)
            .defineWrapperFunctionInvocationAndMockReturnValueTransformation(wrapper -> wrapper.removed(this), identity())
            .expectWrapperToWrapMockFunctionReturnValue()
            .doFunctionDelegationCheck();
    }