assertThat(ordered.adjacentNode("target")).isEqualTo("source");
    assertThat(ordered.toString()).isEqualTo("<source -> target>");
  }

  @Test
  public void testUnorderedEndpointPair() {
    EndpointPair<String> unordered = EndpointPair.unordered("chicken", "egg");
    assertThat(unordered.isOrdered()).isFalse();
    assertThat(unordered).containsExactly("chicken", "egg");