assertFalse(networkAsMutableNetwork.addNode(N1));
    assertThat(networkAsMutableNetwork.nodes()).containsExactlyElementsIn(nodes);
  }

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

    addEdge(N1, N2, E12);
    addEdge(N4, N1, E41);
    assertTrue(networkAsMutableNetwork.removeNode(N1));