assertNodeNotInGraphErrorMessage(
        assertThrows(
            IllegalArgumentException.class, () -> network.incidentEdges(NODE_NOT_IN_GRAPH)));
  }

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

  @Test
  public void incidentNodes_edgeNotInGraph() {
    assertEdgeNotInGraphErrorMessage(