private final UnionFileTree set = new UnionFileTree(TestFiles.taskDependencyFactory(), "<display name>")

    def setup() {
        NativeServicesTestFixture.initialize()
    }

    def canAddFileTree() {
        FileTreeInternal set1 = Mock(FileTreeInternal)
        when:
        set.addToUnion(set1)

        then:
        set.sourceCollections == [set1]
    }

    def cannotAddFileCollection() {