graph.putEdgeValue(2, 3, "valueC");

    assertThat(graph.removeEdge(1, 2)).isEqualTo("valueA");
    assertThat(graph.removeEdge(1, 2)).isNull();
    assertThat(graph.removeEdge(2, 1)).isEqualTo("valueB");
    assertThat(graph.removeEdge(2, 1)).isNull();
    assertThat(graph.removeEdge(2, 3)).isEqualTo("valueC");
    assertThat(graph.removeEdge(2, 3)).isNull();
  }

  @Test
  public void removeEdge_undirected() {

    graph.putEdgeValue(2, 3, "valueC");

    assertThat(graph.removeEdge(1, 2)).isEqualTo("valueA");
    assertThat(graph.removeEdge(1, 2)).isNull();
    assertThat(graph.removeEdge(2, 1)).isEqualTo("valueB");
    assertThat(graph.removeEdge(2, 1)).isNull();
    assertThat(graph.removeEdge(2, 3)).isEqualTo("valueC");
    assertThat(graph.removeEdge(2, 3)).isNull();
  }

  @Test
  public void removeEdge_undirected() {

    return backingValueGraph.removeNode(node);
  }

  @Override
  public boolean removeEdge(N nodeU, N nodeV) {
    return backingValueGraph.removeEdge(nodeU, nodeV) != null;
  }

  @Override
  public boolean removeEdge(EndpointPair<N> endpoints) {
    validateEndpoints(endpoints);
    return removeEdge(endpoints.nodeU(), endpoints.nodeV());
  }

  }

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

    addEdge(N1, N2, E12);
    assertTrue(networkAsMutableNetwork.removeEdge(E12));
    assertFalse(networkAsMutableNetwork.removeEdge(E12));
    assertThat(networkAsMutableNetwork.edges()).doesNotContain(E12);
    assertThat(networkAsMutableNetwork.edgesConnecting(N1, N2)).isEmpty();
  }

  @Test

    assume().that(graphIsMutable()).isTrue();

    putEdge(N1, N2);
    putEdge(N2, N1); // no-op

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

  @Test
  public void removeNode_existingNodeWithSelfLoopEdge() {

        if (cycle != null) {
            // remove edge which introduced cycle
            removeEdge(from, to);
            throw new CycleDetectedException(
                    "Edge between '" + from.label + "' and '" + to.label + "' introduces to cycle in the graph", cycle);
        }
    }

    void removeEdge(Vertex from, Vertex to) {
        from.children.remove(to);
        to.parents.remove(from);
    }

    putEdge(N1, N2);
    assertThat(graph.successors(N1)).containsExactly(N2);
    assertThat(graph.predecessors(N2)).containsExactly(N1);
    assertThat(graphAsMutableGraph.removeEdge(N1, N2)).isTrue();
    assertThat(graphAsMutableGraph.removeEdge(N1, N2)).isFalse();
    assertThat(graph.successors(N1)).isEmpty();
    assertThat(graph.predecessors(N2)).isEmpty();
  }

  @Test
  public void removeEdge_oneOfMany() {

    assume().that(graphIsMutable()).isTrue();

    putEdge(N1, N2);
    putEdge(N2, N1); // no-op

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

  @Test
  public void removeNode_existingNodeWithSelfLoopEdge() {

   *
   * @return the value previously associated with the edge connecting {@code nodeU} to {@code
   *     nodeV}, or null if there was no such edge.
   */
  @CanIgnoreReturnValue
  @CheckForNull
  V removeEdge(N nodeU, N nodeV);

  /**
   * Removes the edge connecting {@code endpoints}, if it is present.
   *
   * <p>If this graph is directed, {@code endpoints} must be ordered.
   *

    for (E edge : ImmutableList.copyOf(connections.incidentEdges())) {
      removeEdge(edge);
    }
    nodeConnections.remove(node);
    return true;
  }

  @Override
  @CanIgnoreReturnValue
  public boolean removeEdge(E edge) {
    checkNotNull(edge, "edge");

    N nodeU = edgeToReferenceNode.get(edge);
    if (nodeU == null) {
      return false;