public void incidentEdges_nodeNotInGraph() {
    assertNodeNotInGraphErrorMessage(
        assertThrows(IllegalArgumentException.class, () -> graph.incidentEdges(NODE_NOT_IN_GRAPH)));
  }

  @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);