assertThat(n2Successors).isEmpty();
    assertThat(n2IncidentEdges).isEmpty();
    assertThat(n2InEdges).isEmpty();
    assertThat(n2OutEdges).isEmpty();
  }

  @Test
  public void removeEdge_existingEdge() {
    assume().that(graphIsMutable()).isTrue();

    addEdge(N1, N2, E12);
    assertTrue(networkAsMutableNetwork.removeEdge(E12));
    assertFalse(networkAsMutableNetwork.removeEdge(E12));