Assert.assertNotNull(vertex);
Assert.assertEquals(vertex.getValue(), "a");
Assert.assertNull(graph.getVertex("1"));
Edge edge = graph.getEdge("a", "b");
Assert.assertNotNull(edge);
Assert.assertEquals(edge.getWeight(), 3);
edge = graph.getEdge("b", "a");
Assert.assertNull(edge);
DirectedGraph<String, Object>.Path path = graph.getShortestPath("a", "c");