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

    putEdge(N1, N2);
    putEdge(N1, N3);
    putEdge(N1, N4);
    assertThat(graphAsMutableGraph.removeEdge(N1, N3)).isTrue();
    assertThat(graph.adjacentNodes(N1)).containsExactly(N2, N4);
  }

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

    putEdge(N1, N2);

    expectedClosure.putEdge(N2, N2);
    expectedClosure.putEdge(N2, N3);
    expectedClosure.putEdge(N2, N4);
    expectedClosure.putEdge(N3, N1);
    expectedClosure.putEdge(N3, N2);
    expectedClosure.putEdge(N3, N3);
    expectedClosure.putEdge(N3, N4);
    expectedClosure.putEdge(N4, N1);
    expectedClosure.putEdge(N4, N2);
    expectedClosure.putEdge(N4, N3);
    expectedClosure.putEdge(N4, N4);

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

    putEdge(N1, N2);
    putEdge(N1, N3);
    putEdge(N1, N4);
    assertThat(graphAsMutableGraph.removeEdge(N1, N3)).isTrue();
    assertThat(graph.adjacentNodes(N1)).containsExactly(N2, N4);
  }

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

    putEdge(N1, N2);

    MutableGraph<String> graph = GraphBuilder.directed().build();
    graph.putEdge("a", "b");

    Traverser.forTree(graph); // Does not throw
  }

  @Test
  public void forTree_withUndirectedGraph_throws() throws Exception {
    MutableGraph<String> graph = GraphBuilder.undirected().build();
    graph.putEdge("a", "b");

    assertThrows(IllegalArgumentException.class, () -> Traverser.forTree(graph));

        }

        orderedNodeConnectionsBuilder.add(new NodeConnection.Pred<>(predecessor));
        predecessorCount++;
      } else { // incidentEdge is an outEdge
        checkArgument(incidentEdge.nodeU().equals(thisNode));

        N successor = incidentEdge.nodeV();
        V value = successorNodeToValueFn.apply(successor);