def set2 = of([artifact1])

        when:
        set1.artifacts.visit(visitor)

        then:
        1 * visitor.visitArtifacts(_) >> { ResolvedArtifactSet.Artifacts artifacts ->
            artifacts.startFinalization(queue, false)
            artifacts.visit(artifactVisitor)
        }
        1 * artifactVisitor.requireArtifactFiles() >> false

        artifacts.size() == 1
        1 * artifacts.visit(_) >> { ArtifactVisitor visitor -> visitor.visitArtifact(null, null, ImmutableCapabilities.EMPTY, artifact) }
        0 * _

        when:
        artifacts[0].startFinalization(operationQueue, true)

        then:
        1 * transformStep.createInvocation(_, _, _) >> invocation
        1 * invocation.getCompleted() >> Optional.empty()
        1 * operationQueue.add(_ as BuildOperation)

    private final Throwable failure;

    public BrokenArtifacts(Throwable failure) {
        this.failure = failure;
    }

    @Override
    public void startFinalization(BuildOperationQueue<RunnableBuildOperation> actions, boolean requireFiles) {
    }

    @Override
    public void visit(ArtifactVisitor visitor) {
        visitor.visitFailure(failure);
    }

    }

    @Override
    public void visitExternalArtifacts(Action<ResolvableArtifact> visitor) {
        throw UncheckedException.throwAsUncheckedException(failure);
    }

    @Override
    public void startFinalization(BuildOperationQueue<RunnableBuildOperation> actions, boolean requireFiles) {
    }

    @Override
    public void visit(ArtifactVisitor visitor) {
        visitor.visitFailure(failure);
    }

    private final FileCollectionInternal.Source source;

    public EndCollection(FileCollectionInternal.Source source) {
        this.source = source;
    }

    @Override
    public void startFinalization(BuildOperationQueue<RunnableBuildOperation> actions, boolean requireFiles) {
    }

    @Override
    public void visit(ArtifactVisitor visitor) {
        visitor.endVisitCollection(source);
    }

            @Override
            public void visit(Visitor visitor) {
                visitor.visitArtifacts(new Artifacts() {
                    @Override
                    public void startFinalization(BuildOperationQueue<RunnableBuildOperation> actions, boolean requireFiles) {
                        // Nothing to do
                    }

                    @Override

                return visitor.prepareForVisit(source);
            }

            @Override
            public void visitArtifacts(ResolvedArtifactSet.Artifacts artifacts) {
                artifacts.startFinalization(queue, visitor.requireArtifactFiles());
                results.add(artifacts);
            }

            @Override
            public void execute(BuildOperationQueue<RunnableBuildOperation> buildOperationQueue) {

            visitor.visitArtifacts(new EndCollection(this));
        } else {
            visitor.visitArtifacts(this);
        }
    }

    @Override
    public void startFinalization(BuildOperationQueue<RunnableBuildOperation> actions, boolean requireFiles) {
        // TODO - should add any nodes that have not been executed
    }

    @Override
    public void visit(ArtifactVisitor visitor) {

         */
        default void prepareForVisitingIfNotAlready() {}

        /**
         * Queues up any work still remaining to finalize the set of artifacts contained in this set.
         */
        void startFinalization(BuildOperationQueue<RunnableBuildOperation> actions, boolean requireFiles);

        /**

    }

    @Override
    public void visit(Visitor visitor) {
        visitor.visitArtifacts(this);
    }

    @Override
    public void startFinalization(BuildOperationQueue<RunnableBuildOperation> actions, boolean requireFiles) {
    }

    @Override
    public void visit(ArtifactVisitor visitor) {
        for (final ResolvedArtifact artifact : artifacts) {