### Question:
MultiGraph implements Graph { public Vertex addVertex(Object id) { throw new UnsupportedOperationException(READONLY_MSG); } MultiGraph(final Graph... bases); Vertex addVertex(Object id); Vertex getVertex(Object id); void removeVertex(Vertex vertex); Edge addEdge(Object id, Vertex outVertex, Vertex inVertex, String label); Edge getEdge(Object id); void removeEdge(Edge edge); Iterable<Vertex> getVertices(); Iterable<Edge> getEdges(); void clear(); void shutdown();  }### Answer:
@Test(expected = UnsupportedOperationException.class) public void testAddVertexUnsupported() throws Exception { graph.addVertex(null); }