/**
     * Adds an edge connecting {@code endpoints} (in the order, if any, specified by {@code
     * endpoints}) if one is not already present.
     *
     * <p>If this graph is directed, {@code endpoints} must be ordered and the added edge will be
     * directed; if it is undirected, the added edge will be undirected.
     *
     * <p>If this graph is directed, {@code endpoints} must be ordered.
     *

     * must also be non-null.
     *
     * <p>If either or both endpoints are not already present in this network, this method will
     * silently {@link #addNode(Object) add} each missing endpoint to the network.
     *
     * <p>If {@code edge} already connects an endpoint pair equal to {@code endpoints}, then this
     * method will have no effect.
     *
     * @return this {@code Builder} object

   * Returns the value of the edge that connects {@code endpoints} (in the order, if any, specified
   * by {@code endpoints}), if one is present; otherwise, returns {@code defaultValue}.
   *
   * <p>If this graph is directed, the endpoints must be ordered.
   *
   * @throws IllegalArgumentException if either endpoint is not an element of this graph
   * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed

  /**
   * Adds an edge connecting {@code endpoints} (in the order, if any, specified by {@code
   * endpoints}) if one is not already present.
   *
   * <p>If this graph is directed, {@code endpoints} must be ordered and the added edge will be
   * directed; if it is undirected, the added edge will be undirected.
   *
   * <p>If this graph is directed, {@code endpoints} must be ordered.
   *

  public boolean hasEdgeConnecting(EndpointPair<N> endpoints) {
    return delegate().hasEdgeConnecting(endpoints);
  }

  @Override
  @CheckForNull
  public V edgeValueOrDefault(N nodeU, N nodeV, @CheckForNull V defaultValue) {
    return delegate().edgeValueOrDefault(nodeU, nodeV, defaultValue);
  }

  @Override
  @CheckForNull
  public V edgeValueOrDefault(EndpointPair<N> endpoints, @CheckForNull V defaultValue) {

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

    EndpointPair<Integer> endpoints = EndpointPair.unordered(N1, N2);
    IllegalArgumentException e =
        assertThrows(IllegalArgumentException.class, () -> graphAsMutableGraph.putEdge(endpoints));
    assertThat(e).hasMessageThat().contains(ENDPOINTS_MISMATCH);
  }

  /**

    checkNotNull(endpoints);
    checkArgument(isOrderingCompatible(endpoints), ENDPOINTS_MISMATCH);
  }

  /**
   * Returns {@code true} iff {@code endpoints}' ordering is compatible with the directionality of
   * this graph.
   */
  protected final boolean isOrderingCompatible(EndpointPair<?> endpoints) {
    return endpoints.isOrdered() == this.isDirected();
  }

    }
    return previousValue;
  }

  @Override
  @CanIgnoreReturnValue
  @CheckForNull
  public V putEdgeValue(EndpointPair<N> endpoints, V value) {
    validateEndpoints(endpoints);
    return putEdgeValue(endpoints.nodeU(), endpoints.nodeV(), value);
  }

  @Override
  @CanIgnoreReturnValue
  public boolean removeNode(N node) {
    checkNotNull(node, "node");

    assertThat(e).hasMessageThat().contains(ENDPOINTS_MISMATCH);
    e =
        assertThrows(
            IllegalArgumentException.class, () -> graph.edgeValue(EndpointPair.unordered(2, 1)));
    assertThat(e).hasMessageThat().contains(ENDPOINTS_MISMATCH);
  }

  @Test
  public void edgeValue_undirected_correct() {

  }

  @Override
  public boolean hasEdgeConnecting(EndpointPair<N> endpoints) {
    checkNotNull(endpoints);
    return isOrderingCompatible(endpoints)
        && hasEdgeConnectingInternal(endpoints.nodeU(), endpoints.nodeV());
  }

  @Override
  @CheckForNull
  public V edgeValueOrDefault(N nodeU, N nodeV, @CheckForNull V defaultValue) {