// source node and the second is the target node
    assertThat(network.edgesConnecting(N2, N1)).isEmpty();
  }

  @Test
  public void inEdges_oneEdge() {
    addEdge(N1, N2, E12);
    assertThat(network.inEdges(N2)).containsExactly(E12);
    // Edge direction handled correctly
    assertThat(network.inEdges(N1)).isEmpty();
  }

  @Test

    // source node and the second is the target node
    assertThat(network.edgesConnecting(N2, N1)).isEmpty();
  }

  @Test
  public void inEdges_oneEdge() {
    addEdge(N1, N2, E12);
    assertThat(network.inEdges(N2)).containsExactly(E12);
    // Edge direction handled correctly
    assertThat(network.inEdges(N1)).isEmpty();
  }

  @Test

    addEdge(N1, N2, E12);
    assertThat(network.edgesConnecting(N1, N2)).containsExactly(E12);
    assertThat(network.edgesConnecting(N2, N1)).containsExactly(E12);
  }

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

  @Test
  public void outEdges_oneEdge() {