assertThat(Strings.commonPrefix("xyz", "abcde")).isEqualTo("");
    assertThat(Strings.commonPrefix("xyz", "abcxyz")).isEqualTo("");
    assertThat(Strings.commonPrefix("abc", "aaaaa")).isEqualTo("a");
    assertThat(Strings.commonPrefix("aa", "aaaaa")).isEqualTo("aa");
    assertThat(Strings.commonPrefix(new StringBuilder("abcdef"), "abcxyz")).isEqualTo("abc");

    // Identical valid surrogate pairs.

    assertThat(Strings.commonPrefix("xyz", "abcde")).isEqualTo("");
    assertThat(Strings.commonPrefix("xyz", "abcxyz")).isEqualTo("");
    assertThat(Strings.commonPrefix("abc", "aaaaa")).isEqualTo("a");
    assertThat(Strings.commonPrefix("aa", "aaaaa")).isEqualTo("aa");
    assertThat(Strings.commonPrefix(new StringBuilder("abcdef"), "abcxyz")).isEqualTo("abc");

    // Identical valid surrogate pairs.

  private static final String ALMOST_TOO_MANY_LEVELS = Strings.repeat("a.", 127);

  @SuppressWarnings("InlineMeInliner") // String.repeat unavailable under Java 8
  private static final String ALMOST_TOO_LONG = Strings.repeat("aaaaa.", 40) + "1234567890.c";

  private static final ImmutableSet<String> VALID_NAME =
      ImmutableSet.of(
          // keep-sorted start
          "123.cn",
          "8server.shop",
          "a" + DELTA + "b.com",

  private static final String ALMOST_TOO_MANY_LEVELS = Strings.repeat("a.", 127);

  @SuppressWarnings("InlineMeInliner") // String.repeat unavailable under Java 8
  private static final String ALMOST_TOO_LONG = Strings.repeat("aaaaa.", 40) + "1234567890.c";

  private static final ImmutableSet<String> VALID_NAME =
      ImmutableSet.of(
          // keep-sorted start
          "123.cn",
          "8server.shop",
          "a" + DELTA + "b.com",

                        mapEntry("x", 1),
                        mapEntry("xxx", 3),
                        mapEntry("xx", 2),
                        mapEntry("xxxx", 4),
                        mapEntry("aaaaa", 5));
                  }

                  @Override
                  public Map<String, Integer> create(Object... elements) {
                    Set<String> set = new LinkedHashSet<>();