assertThat(graph.adjacentNodes(N1)).isEmpty();
    assertThat(graph.edges()).isEmpty();
    assertThat(graphAsMutableGraph.removeEdge(N2, N1)).isFalse();
  }

  @Test
  public void removeNode_existingNodeWithSelfLoopEdge() {
    assume().that(graphIsMutable()).isTrue();
    assume().that(graph.allowsSelfLoops()).isTrue();

    addNode(N1);
    putEdge(N1, N1);

    assertTrue(networkAsMutableNetwork.addEdge(N1, N1, E11_A));
    assertThat(network.edgesConnecting(N1, N1)).containsExactly(E11, E11_A);
  }

  @Test
  public void removeNode_existingNodeWithSelfLoopEdge() {
    assume().that(graphIsMutable()).isTrue();
    assume().that(network.allowsSelfLoops()).isTrue();

    addNode(N1);
    addEdge(N1, N1, E11);