assertThat(graphAsMutableGraph.addNode(N1)).isFalse();
    assertThat(graph.nodes()).containsExactlyElementsIn(nodes);
  }

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

    putEdge(N1, N2);
    putEdge(N4, N1);
    assertThat(graphAsMutableGraph.removeNode(N1)).isTrue();

    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));