@Test
  public void convertListOfSpeciesReferenceInSetOfVertices() {
    Connector connector = Connector.makeConnector();
    Model sbmlModel = new Model();

    Species reactant1 = sbmlModel.createSpecies("id1");
    Species reactant2 = sbmlModel.createSpecies("id2");

    Reaction reaction = sbmlModel.createReaction("reaction_id");

    // I'll use the reactants list just because I want a list of
    // species references to work with
    reaction.createReactant(reactant1);
    reaction.createReactant(reactant2);

    final Set<Vertex> collectedVertices = new HashSet<Vertex>();

    Vertex outSide = VertexFactory.makeSimpleVertex();

    Set<Vertex> vertices =
        connector.convertToVertexSet(
            reaction.getListOfReactants(),
            new HashMap<Vertex, Vertex>(),
            new VertexHandlingListener() {

              @Override
              public void vertexHandled(Vertex vertex) {
                collectedVertices.add(vertex);
              }
            });

    // here I repeat the control on the size because I'm using a different
    // overload of the test below.
    assertEquals(2, vertices.size());
    assertEquals(2, collectedVertices.size());

    assertEquals(collectedVertices, vertices);
    assertFalse(vertices.contains(outSide));
  }