}

    public static class TestBuildOperationQueue<O extends RunnableBuildOperation> implements BuildOperationQueue<O> {

        public final BuildOperationRunner runner;

        public TestBuildOperationQueue() {
            this(new TestBuildOperationRunner());
        }

        private TestBuildOperationQueue(BuildOperationRunner runner) {
            this.runner = runner;
        }

    def attributes = Mock(AttributeContainerInternal)
    def variantDisplayName = Describables.of("<variant>")
    def id = Mock(VariantResolveMetadata.Identifier)
    def queue = new TestBuildOperationExecutor.TestBuildOperationQueue()
    def artifact1 = Mock(TestArtifact)
    def artifact2 = Mock(TestArtifact)

    def "visits empty variant"() {
        def visitor = Mock(ResolvedArtifactSet.Visitor)
        def set1 = of([])