// Pause in step 2.
    step2Waiter.awaitStarted();

    // Everything should still be open.
    assertStillOpen(closeable1, closeable2, closeable3, closeable4);

    // Cancel step 3, resume step 2, and pause in step 4.
    assertWithMessage("step3.cancel()").that(step3.cancel(false)).isTrue();
    step2Waiter.awaitReturned();
    step4Waiter.awaitStarted();

    // Pause in step 2.
    step2Waiter.awaitStarted();

    // Everything should still be open.
    assertStillOpen(closeable1, closeable2, closeable3, closeable4);

    // Cancel step 3, resume step 2, and pause in step 4.
    assertWithMessage("step3.cancel()").that(step3.cancel(false)).isTrue();
    step2Waiter.awaitReturned();
    step4Waiter.awaitStarted();

    assume().that(network.allowsSelfLoops()).isTrue();
    assume().that(network.allowsParallelEdges()).isTrue();

    assertTrue(networkAsMutableNetwork.addEdge(N1, N1, E11));
    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();
    assume().that(network.allowsParallelEdges()).isTrue();

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

  @Test
  public void removeNode_existingNodeWithSelfLoopEdge() {

  }

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

    assertThat(graphAsMutableGraph.addNode(N1)).isTrue();
    assertThat(graph.nodes()).contains(N1);
  }

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

    addNode(N1);

        return Streams.findLast(stream);
      }
    },
    REDUCE_LAST {
      @Override
      Object operate(Stream<?> stream) {
        return stream.reduce((a, b) -> b);
      }
    },
    REDUCE_LAST_PARALLEL {
      @Override
      Object operate(Stream<?> stream) {
        return stream.parallel().reduce((a, b) -> b);
      }
    };

    abstract Object operate(Stream<?> stream);
  }

   *
   * <p>This method (dangerously) assume that the strings {@code "!! a"} and {@code "~~ z"} will
   * work for this purpose, which may cause problems for navigable maps with non-string or unicode
   * generators.
   */
  private List<String> getExtremeValues() {
    List<String> result = new ArrayList<>();
    result.add("!! a");
    result.add("!! b");
    result.add("~~ y");
    result.add("~~ z");

   *
   * <p>This method (dangerously) assume that the strings {@code "!! a"} and {@code "~~ z"} will
   * work for this purpose, which may cause problems for navigable maps with non-string or unicode
   * generators.
   */
  private List<String> getExtremeValues() {
    List<String> result = new ArrayList<>();
    result.add("!! a");
    result.add("!! b");
    result.add("~~ y");
    result.add("~~ z");

        .forEachEntry((element, count) -> actual.add(Multisets.immutableEntry(element, count)));
    assertEquals(expected, actual);
  }

  /**
   * Returns {@link Method} instances for the remove tests that assume multisets support duplicates
   * so that the test of {@code Multisets.forSet()} can suppress them.
   */
  @J2ktIncompatible
  @GwtIncompatible // reflection

            interfaceClasses.toArray(new Class<?>[interfaceClasses.size()]),
            new DummyHandler(interfaceType));
    @SuppressWarnings("unchecked") // interfaceType is T
    T result = (T) dummy;
    return result;
  }

  /** Returns the dummy return value for {@code returnType}. */
  abstract <R> @Nullable R dummyReturnValue(TypeToken<R> returnType);