}

  @Test
  public void degree_oneEdge() {
    putEdge(N1, N2);
    assertThat(graph.degree(N1)).isEqualTo(1);
    assertThat(graph.degree(N2)).isEqualTo(1);
  }

  @Test
  public void degree_isolatedNode() {
    addNode(N1);
    assertThat(graph.degree(N1)).isEqualTo(0);
  }

  @Test
  public void degree_nodeNotInGraph() {
    assertNodeNotInGraphErrorMessage(