NetworkBuilder.directed().allowsSelfLoops(true).build();
    mutableNetwork.addEdge("A", "A", "AA");
    mutableNetwork.addEdge("A", "B", "AB");
    Network<String, String> network = ImmutableNetwork.copyOf(mutableNetwork);

    assertThat(network.edgesConnecting("A", "A")).containsExactly("AA");
    assertThat(network.edgesConnecting("A", "B")).containsExactly("AB");

   *  / \\
   * b   c
   *  \ /
   *   d<>
   * }</pre>
   *
   * {@code <>} indicates a self-loop
   */
  private static final SuccessorsFunction<Character> MULTI_GRAPH =
      createDirectedGraph("aa", "dd", "ab", "ac", "ca", "cd", "bd");

  /** A directed graph with a single cycle: a -> b -> c -> d -> a. */
  private static final SuccessorsFunction<Character> CYCLE_GRAPH =
      createDirectedGraph("ab", "bc", "cd", "da");

    ImmutableList<String> empty = ImmutableList.of();
    ImmutableList<String> a = ImmutableList.of("a");
    ImmutableList<String> aa = ImmutableList.of("a", "a");
    ImmutableList<String> ab = ImmutableList.of("a", "b");
    ImmutableList<String> b = ImmutableList.of("b");

    Helpers.testComparator(lexy, empty, a, aa, ab, b);

    new EqualsTester()
        .addEqualityGroup(lexy, ordering.lexicographical())

    ImmutableList<String> empty = ImmutableList.of();
    ImmutableList<String> a = ImmutableList.of("a");
    ImmutableList<String> aa = ImmutableList.of("a", "a");
    ImmutableList<String> ab = ImmutableList.of("a", "b");
    ImmutableList<String> b = ImmutableList.of("b");

    Helpers.testComparator(lexy, empty, a, aa, ab, b);

    new EqualsTester()
        .addEqualityGroup(lexy, ordering.lexicographical())

aaaa.aaa/. aaaa.aaa
aaaa.aaa// aaaa.aaa
aaaa.aa.aa aaaa.aa.aa
aaaa.aa.a. aaaa.aa.a.
aaaa.aa.a/ aaaa.aa.a
aaaa.aa..a aaaa.aa..a
aaaa.aa... aaaa.aa...
aaaa.aa../ aaaa.aa..
aaaa.aa./a aaaa.aa./a
aaaa.aa./. aaaa.aa.
aaaa.aa.// aaaa.aa.
aaaa.aa/aa aaaa.aa/aa
aaaa.aa/a. aaaa.aa/a.
aaaa.aa/a/ aaaa.aa/a
aaaa.aa/.a aaaa.aa/.a
aaaa.aa/.. .
aaaa.aa/./ aaaa.aa
aaaa.aa//a aaaa.aa/a
aaaa.aa//. aaaa.aa
aaaa.aa/// aaaa.aa

/b/c/aaaa.aaa// /b/c/aaaa.aaa
/b/c/aaaa.aa.aa /b/c/aaaa.aa.aa
/b/c/aaaa.aa.a. /b/c/aaaa.aa.a.
/b/c/aaaa.aa.a/ /b/c/aaaa.aa.a
/b/c/aaaa.aa..a /b/c/aaaa.aa..a
/b/c/aaaa.aa... /b/c/aaaa.aa...
/b/c/aaaa.aa../ /b/c/aaaa.aa..
/b/c/aaaa.aa./a /b/c/aaaa.aa./a
/b/c/aaaa.aa./. /b/c/aaaa.aa.
/b/c/aaaa.aa.// /b/c/aaaa.aa.
/b/c/aaaa.aa/aa /b/c/aaaa.aa/aa
/b/c/aaaa.aa/a. /b/c/aaaa.aa/a.
/b/c/aaaa.aa/a/ /b/c/aaaa.aa/a

    assertEquals("", Strings.commonPrefix("xyz", "abcde"));
    assertEquals("", Strings.commonPrefix("xyz", "abcxyz"));
    assertEquals("a", Strings.commonPrefix("abc", "aaaaa"));
    assertEquals("aa", Strings.commonPrefix("aa", "aaaaa"));
    assertEquals("abc", Strings.commonPrefix(new StringBuffer("abcdef"), "abcxyz"));

    // Identical valid surrogate pairs.
    assertEquals(

   *  / \\
   * b   c
   *  \ /
   *   d<>
   * }</pre>
   *
   * {@code <>} indicates a self-loop
   */
  private static final SuccessorsFunction<Character> MULTI_GRAPH =
      createDirectedGraph("aa", "dd", "ab", "ac", "ca", "cd", "bd");

  /** A directed graph with a single cycle: a -> b -> c -> d -> a. */
  private static final SuccessorsFunction<Character> CYCLE_GRAPH =
      createDirectedGraph("ab", "bc", "cd", "da");

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                  @Override
                  public SampleElements<Entry<String, Integer>> samples() {
                    return new SampleElements<>(
                        mapEntry("a", 1),
                        mapEntry("aa", 2),
                        mapEntry("aba", 3),
                        mapEntry("bbbb", 4),
                        mapEntry("ccccc", 5));
                  }

                  @Override