given:
        container.add(a)

        when:
        container.add(a)

        then:
        toList(container) == [a]

        when:
        container.addAll([a, b])

        then:
        toList(container) == [a, b]
    }

    def "element added using provider is not realized when added"() {
        containerAllowsExternalProviders()

    fromList.add(2, 9);
    assertEquals(asList(6, 4, 3, 9, 2, 5), toList);
    fromList.remove(Integer.valueOf(2));
    assertEquals(asList(6, 4, 3, 9, 5), toList);
    fromList.remove(3);
    assertEquals(asList(6, 3, 9, 5), toList);

    /* toList modifications reflected in fromList */
    toList.remove(0);
    assertEquals(asList(5, 9, 3), fromList);
    toList.add(7);
    assertEquals(asList(7, 5, 9, 3), fromList);

    fromList.add(2, 9);
    assertEquals(asList(6, 4, 3, 9, 2, 5), toList);
    fromList.remove(Integer.valueOf(2));
    assertEquals(asList(6, 4, 3, 9, 5), toList);
    fromList.remove(3);
    assertEquals(asList(6, 3, 9, 5), toList);

    /* toList modifications reflected in fromList */
    toList.remove(0);
    assertEquals(asList(5, 9, 3), fromList);
    toList.add(7);
    assertEquals(asList(7, 5, 9, 3), fromList);

     */
    public static String toArray(List<String> list) {
        return list == null ? null : "(" + String.join(",", list) + ")";
    }

    public static List<String> toList(Object[] objects) {
        return Stream.of(objects).map(Object::toString).map(String::trim).collect(Collectors.toList());
    }

    /**

    }

    def "composite containing one collection"() {
        expect:
        composite(collection("a", "b")).toList() == ["a", "b"]
    }

    def "composite containing two collections"() {
        expect:
        composite(collection("a", "b"), collection("c", "d")).toList() == ["a", "b", "c", "d"]
    }

    def "combined collection contains additions and removals"() {
        given:

    @Test public void canOverwriteProperties() {
        final List conventionList1 = toList("a");
        conventionAware.map("list1", new Callable<Object>() {
            public Object call() {
                return conventionList1;
            }
        });
        assertSame(conventionList1, conventionAware.getConventionValue(null, "list1", false));
        List expectedList1 = toList("b");

        List<GenerationResult> results = generators.stream().map(generators -> generators.generateCodeForRequestedInterceptors(interceptionRequests)).collect(Collectors.toList());

        List<HasFailures> failures = results.stream().filter(it -> it instanceof HasFailures).map(it -> (HasFailures) it).collect(Collectors.toList());
        if (!failures.isEmpty()) {

        def testClosure = {
            return it != "b"
        }

        container.add("a")
        container.add("b")
        container.add("c")

        expect:
        toList(container.matching(spec)) == ["a", "c"]
        toList(container.matching(testClosure)) == ["a", "c"]
    }

    def filteredCollectionIsLive() {
        def spec = new Spec<CharSequence>() {
            boolean isSatisfiedBy(CharSequence element) {

    }

    protected static @Nullable <T> List<T> rationalizeInput(@Nullable T[] arguments) {
        return arguments != null && arguments.length > 0 ? Arrays.asList(arguments) : null;
    }

    protected static @Nullable <T> List<T> rationalizeInput(@Nullable Iterable<? extends T> arguments) {
        return arguments != null && arguments.iterator().hasNext() ? CollectionUtils.toList(arguments) : null;
    }

    @Override

        rootDir.file("subdir2/file2.txt").write("content");
        archiveFileToRoot(getArchiveFile());

        assertVisits(getTree(), toList("subdir/file1.txt", "subdir2/file2.txt"), toList("subdir", "subdir2"));
        assertSetContainsForAllTypes(getTree(), toList("subdir/file1.txt", "subdir2/file2.txt"));
    }

    @Test
    public void canStopVisitingFiles() {