graph.addVertex("a");
        assertEquals(1, graph.getVertices().size());
        assertEquals("a", graph.getVertex("a").getLabel());
        graph.addVertex("a");
        assertEquals(1, graph.getVertices().size());
        assertEquals("a", graph.getVertex("a").getLabel());

        graph.addVertex("b");
        assertEquals(2, graph.getVertices().size());
        assertFalse(hasEdge(graph, "a", "b"));

    private MetadataGraph findLinkedSubgraph(MetadataGraph g) {
        if (g.getVertices().size() == 1) {
            return g;
        }

        List<MetadataGraphVertex> visited = new ArrayList<>(g.getVertices().size());
        visit(g.getEntry(), visited, g);

        List<MetadataGraphVertex> dropList = new ArrayList<>(g.getVertices().size());

        // collect drop list

        protected ClasspathGraphVisitor(MetadataGraph cleanGraph, ClasspathContainer cpc) {
            this.cpc = cpc;
            this.graph = cleanGraph;

            visited = new ArrayList<>(cleanGraph.getVertices().size());
        }

        // -----------------------------------------------------------------------
        protected void visit(MetadataGraphVertex node) {
            ArtifactMetadata md = node.getMd();

    public MetadataGraphVertex getEntry() {
        return entry;
    }

    public void setEntry(MetadataGraphVertex entry) {
        this.entry = entry;
    }

    public TreeSet<MetadataGraphVertex> getVertices() {
        return vertices;
    }

    public List<MetadataGraphEdge> getIncidentEdges(MetadataGraphVertex vertex) {
        checkEdges();
        return incidentEdges.get(vertex);
    }