assertEquals(StringLength.COMPARATOR, keySet.comparator());
    assertEquals(Sets.<@Nullable String>newHashSet(null, "tree"), keySet.headSet("yahoo"));
    assertEquals(newHashSet("google"), keySet.tailSet("yahoo"));
    assertEquals(newHashSet("tree"), keySet.subSet("ask", "yahoo"));
  }

  @GwtIncompatible // SerializableTester
  public void testExplicitComparatorSerialization() {

          "foo.blogspot.co.uk",
          "foo.uk.com",
          "foo.bar.co.il",
          "state.CA.us",
          "www.state.pa.us",
          "pvt.k12.ca.us",
          "www.google.com",
          "www4.yahoo.co.uk",
          "home.netscape.com",
          "web.MIT.edu",
          "foo.eDu.au",
          "utenti.blah.IT",
          "dominio.com.co");

  private static final ImmutableSet<String> NON_RS =

*   Added `tf.Session.make_callable()`, which provides a lower overhead means of
    running a similar step multiple times.
*   Added libverbs-based RDMA support to contrib (courtesy @junshi15 from
    Yahoo).
*   Bring `tf.feature_column.*` into the API. Non-deprecated functionality from
    `tf.contrib.layers.*` is moved to `tf.feature_column.*` with cosmetic
    changes.