String unused = network.edgeConnectingOrNull(ENDPOINTS_N1N2);
            });
    assertThat(e).hasMessageThat().contains(ENDPOINTS_MISMATCH);
  }

  @Test
  public void edgesConnecting_oneEdge() {
    addEdge(N1, N2, E12);
    assertThat(network.edgesConnecting(N1, N2)).containsExactly(E12);
    assertThat(network.edgesConnecting(N2, N1)).containsExactly(E12);
  }

  @Test