Network<Integer, String> copy = copyOf(undirectedGraph);
    assertThat(copy).isEqualTo(undirectedGraph);
  }

  // Graph creation tests

  @Test
  public void createDirected() {
    MutableNetwork<Integer, String> directedGraph = NetworkBuilder.directed().build();
    assertThat(directedGraph.nodes()).isEmpty();
    assertThat(directedGraph.edges()).isEmpty();