assertThat(network.nodes()).containsExactly("A");
    assertThat(network.edges()).isEmpty();
  }

  @Test
  public void immutableNetworkBuilder_putEdgeFromNodes() {
    ImmutableNetwork<String, Integer> network =
        NetworkBuilder.directed().<String, Integer>immutable().addEdge("A", "B", 10).build();

    assertThat(network.nodes()).containsExactly("A", "B");