final FileVisitor visitor = Mock()

        when:
        tree.visit(visitor)

        then:
        1 * source1.visit(visitor)
        1 * source2.visit(visitor)
    }

    def visitsEachTreeWithClosure() {
        final Closure visitor = TestUtil.TEST_CLOSURE
        final FileVisitor closureAsVisitor = DefaultGroovyMethods.asType(visitor, FileVisitor.class)

        when:
        tree.visit(visitor)