assertThat(copy).isEqualTo(undirectedGraph);
  }

  @Test
  public void copyOf_directedNetwork() {
    Network<Integer, String> directedGraph = buildDirectedNetwork();

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

  @Test
  public void copyOf_undirectedNetwork() {