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

    addNode(N1);
    Set<Integer> adjacentNodes = network.adjacentNodes(N1);
    assertThrows(UnsupportedOperationException.class, () -> adjacentNodes.add(N2));
    addEdge(N1, N2, E12);
    assertThat(network.adjacentNodes(N1)).containsExactlyElementsIn(adjacentNodes);
  }

  @Override
  public void adjacentEdges_checkReturnedSetMutability() {

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

    addNode(N1);
    Set<Integer> adjacentNodes = network.adjacentNodes(N1);
    assertThrows(UnsupportedOperationException.class, () -> adjacentNodes.add(N2));
    addEdge(N1, N2, E12);
    assertThat(network.adjacentNodes(N1)).containsExactlyElementsIn(adjacentNodes);
  }

  @Override
  public void adjacentEdges_checkReturnedSetMutability() {

        }
      }

      for (N adjacentNode : sanityCheckSet(network.adjacentNodes(node))) {
        assertTrue(
            network.predecessors(node).contains(adjacentNode)
                || network.successors(node).contains(adjacentNode));
        assertTrue(
            !network.edgesConnecting(node, adjacentNode).isEmpty()
                || !network.edgesConnecting(adjacentNode, node).isEmpty());
      }

          .addEqualityGroup(
              network.predecessors(node), network.successors(node), network.adjacentNodes(node))
          .testEquals();

      for (Integer adjacentNode : network.adjacentNodes(node)) {
        assertThat(network.edgesConnecting(node, adjacentNode))
            .containsExactlyElementsIn(network.edgesConnecting(adjacentNode, node));
      }
    }
  }

  @Override
  @Test

      }

      for (N adjacentNode : sanityCheckSet(graph.adjacentNodes(node))) {
        if (!graph.allowsSelfLoops()) {
          assertThat(node).isNotEqualTo(adjacentNode);
        }
        assertThat(
                graph.predecessors(node).contains(adjacentNode)
                    || graph.successors(node).contains(adjacentNode))
            .isTrue();
      }

          .addEqualityGroup(
              network.predecessors(node), network.successors(node), network.adjacentNodes(node))
          .testEquals();

      for (Integer adjacentNode : network.adjacentNodes(node)) {
        assertThat(network.edgesConnecting(node, adjacentNode))
            .containsExactlyElementsIn(network.edgesConnecting(adjacentNode, node));
      }
    }
  }

  @Override
  @Test

      }

      @Override
      public boolean allowsSelfLoops() {
        return AbstractNetwork.this.allowsSelfLoops();
      }

      @Override
      public Set<N> adjacentNodes(N node) {
        return AbstractNetwork.this.adjacentNodes(node);
      }

      @Override
      public Set<N> predecessors(N node) {
        return AbstractNetwork.this.predecessors(node);
      }

      @Override

      }

      @Override
      public boolean allowsSelfLoops() {
        return AbstractNetwork.this.allowsSelfLoops();
      }

      @Override
      public Set<N> adjacentNodes(N node) {
        return AbstractNetwork.this.adjacentNodes(node);
      }

      @Override
      public Set<N> predecessors(N node) {
        return AbstractNetwork.this.predecessors(node);
      }

      @Override

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

    addNode(N1);
    Set<Integer> adjacentNodes = graph.adjacentNodes(N1);
    assertThrows(UnsupportedOperationException.class, () -> adjacentNodes.add(N2));
    putEdge(N1, N2);
    assertThat(graph.adjacentNodes(N1)).containsExactlyElementsIn(adjacentNodes);
  }

  @Override
  @Test
  public void predecessors_checkReturnedSetMutability() {

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

    addNode(N1);
    Set<Integer> adjacentNodes = graph.adjacentNodes(N1);
    assertThrows(UnsupportedOperationException.class, () -> adjacentNodes.add(N2));
    putEdge(N1, N2);
    assertThat(graph.adjacentNodes(N1)).containsExactlyElementsIn(adjacentNodes);
  }

  @Override
  @Test
  public void predecessors_checkReturnedSetMutability() {