graph = ValueGraphBuilder.directed().build();
    graph.putEdgeValue(1, 2, "A");
    assertThat(graph.edgeValue(EndpointPair.ordered(2, 1))).isEmpty();
  }

  @Test
  public void edgeValue_directed_mismatch() {
    graph = ValueGraphBuilder.directed().build();
    graph.putEdgeValue(1, 2, "A");
    IllegalArgumentException e =
        assertThrows(