FileTreeInternal treeOf(MinimalFileTree tree);

    static FileTreeInternal emptyTree() {
        return EmptyFileTree.INSTANCE;
    }

    static FileTreeInternal emptyTree(String displayName) {
        if (FileTreeInternal.DEFAULT_TREE_DISPLAY_NAME.equals(displayName)) {
            return emptyTree();
        } else {
            return new EmptyFileTree(displayName);
        }
    }

        expect:
        def collection = FileCollectionFactory.empty()
        emptyCollection(collection)
        collection.toString() == "file collection"

        def tree = collection.asFileTree
        emptyTree(tree)
        tree.toString() == "file tree"
    }

    def "constructs empty collection with display name"() {
        expect:
        def collection = FileCollectionFactory.empty("some collection")

    }

    @Override
    public FileTreeInternal treeOf(List<? extends FileTreeInternal> fileTrees) {
        if (fileTrees.isEmpty()) {
            return FileCollectionFactory.emptyTree();
        } else if (fileTrees.size() == 1) {
            return fileTrees.get(0);
        } else {
            return new DefaultCompositeFileTree(taskDependencyFactory, patternSetFactory, ImmutableList.copyOf(fileTrees));