when:
        collection.visitStructure(visitor)

        then:
        1 * visitor.startVisit(_, collection) >> false
        0 * _
    }

    def "getAsFiletrees() returns union of file trees"() {
        def dir1 = tmpDir.createDir("dir1")
        def dir2 = tmpDir.createDir("dir2")
        def source1 = Mock(FileTreeInternal)
        def source2 = Mock(FileTreeInternal)