assertEquals("three", map.higherKey("one"));
    assertEquals("three", map.higherKey("r"));
    assertEquals("three", map.ceilingKey("r"));
    assertEquals("one", map.ceilingKey("one"));
    assertEquals(mapEntry("three", 5), map.higherEntry("one"));
    assertEquals(mapEntry("one", 3), map.ceilingEntry("one"));
    assertEquals("one", map.lowerKey("three"));

    registry.register(o1);

    Iterator<Subscriber> three = registry.getSubscribers("");
    assertEquals(s1, one.next().target);
    assertFalse(one.hasNext());

    assertEquals(s1, three.next().target);
    assertEquals(s2, three.next().target);
    assertEquals(o1, three.next().target);
    assertFalse(three.hasNext());

    three = registry.getSubscribers("");

    registry.unregister(s2);

    assertEquals("three", map.higherKey("one"));
    assertEquals("three", map.higherKey("r"));
    assertEquals("three", map.ceilingKey("r"));
    assertEquals("one", map.ceilingKey("one"));
    assertEquals(mapEntry("three", 5), map.higherEntry("one"));
    assertEquals(mapEntry("one", 3), map.ceilingEntry("one"));
    assertEquals("one", map.lowerKey("three"));

        ImmutableMap.of("one", 1, "two", 2, "three", 3), "one", 1, "two", 2, "three", 3);
    assertMapEquals(
        ImmutableMap.of("one", 1, "two", 2, "three", 3, "four", 4),
        "one",
        1,
        "two",
        2,
        "three",
        3,
        "four",
        4);
    assertMapEquals(
        ImmutableMap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5),
        "one",

  }

  protected void populate(Multimap<String, Integer> multimap) {
    multimap.put("one", 1);
    multimap.put("two", 2);
    multimap.put("two", 22);
    multimap.put("three", 3);
    multimap.put("three", 33);
    multimap.put("three", 333);
  }

  @Override
  protected String getKeyNotInPopulatedMap() throws UnsupportedOperationException {
    return "zero";
  }

  @Override

        new AbstractBiMap<Integer, String>(
            new IdentityHashMap<Integer, String>(), new IdentityHashMap<String, Integer>()) {};
    bimap.put(1, "one");
    bimap.put(2, "two");
    bimap.put(3, "three");
    Iterator<Integer> iterator = bimap.keySet().iterator();
    iterator.next();
    iterator.next();
    iterator.remove();
    iterator.next();
    iterator.remove();
    assertEquals(1, bimap.size());

        Helpers.mapEntry("one", "January"),
        Helpers.mapEntry("two", "February"),
        Helpers.mapEntry("three", "March"),
        Helpers.mapEntry("four", "April"),
        Helpers.mapEntry("five", "May"));
  }

  @Override
  public SampleElements<String> sampleKeys() {
    return new SampleElements<>("one", "two", "three", "four", "five");
  }

  @Override
  public SampleElements<String> sampleValues() {

    assertMultimapEquals(
        ImmutableSetMultimap.of("one", 1, "two", 2, "three", 3, "four", 4),
        "one",
        1,
        "two",
        2,
        "three",
        3,
        "four",
        4);
    assertMultimapEquals(
        ImmutableSetMultimap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5),
        "one",

    Object two = new Object();
    Object three = new Object();
    Object four = new Object();
    Object five = new Object();
    Object six = new Object();

    map.put(one, two);
    map.remove(one);
    assertNotified(listener, one, two, RemovalCause.EXPLICIT);

    map.put(two, three);
    map.remove(two, three);
    assertNotified(listener, two, three, RemovalCause.EXPLICIT);

    map.put(three, four);

    Object two = new Object();
    Object three = new Object();
    Object four = new Object();
    Object five = new Object();
    Object six = new Object();

    map.put(one, two);
    map.remove(one);
    assertNotified(listener, one, two, RemovalCause.EXPLICIT);

    map.put(two, three);
    map.remove(two, three);
    assertNotified(listener, two, three, RemovalCause.EXPLICIT);

    map.put(three, four);