EndpointPair<Integer> endpointPair = network.incidentNodes("1-2");
      assertThrows(IllegalArgumentException.class, () -> endpointPair.adjacentNode(3));
    }
  }

  @Test
  public void testEquals() {
    EndpointPair<String> ordered = EndpointPair.ordered("a", "b");
    EndpointPair<String> orderedMirror = EndpointPair.ordered("b", "a");
    EndpointPair<String> unordered = EndpointPair.unordered("a", "b");

      EndpointPair<Integer> endpointPair = network.incidentNodes("1-2");
      assertThrows(IllegalArgumentException.class, () -> endpointPair.adjacentNode(3));
    }
  }

  @Test
  public void testEquals() {
    EndpointPair<String> ordered = EndpointPair.ordered("a", "b");
    EndpointPair<String> orderedMirror = EndpointPair.ordered("b", "a");
    EndpointPair<String> unordered = EndpointPair.unordered("a", "b");