assertThat(networkForTest.edgesConnecting(N2, N1)).isEmpty();
    } else {
      assertThat(networkForTest.edgesConnecting(N2, N1)).containsExactly(E12);
    }
  }

  @Test
  public void edgesConnecting_selfLoop() {
    network.addEdge(N1, N1, E11);
    assertThat(networkForTest.edgesConnecting(N1, N1)).containsExactly(E11);
    network.addEdge(N1, N2, E12);