}

  public void testOnlyElementNull() {
    assertThat(Stream.<@Nullable Object>of((Object) null).collect(MoreCollectors.onlyElement()))
        .isNull();
  }

  public void testOnlyElementMultiple() {
    try {
      Stream.of(1, 2).collect(MoreCollectors.onlyElement());
      fail("Expected IllegalArgumentException");

        ImmutableSortedSet.copyOf(new String[] {"e", "e", "f", "b", "i", "d", "c", "k"});
    assertThat(set.floor("a")).isNull();
  }

  public void testCeiling_emptySet() {
    ImmutableSortedSet<String> set = ImmutableSortedSet.copyOf(new String[] {});
    assertThat(set.ceiling("f")).isNull();
  }

  public void testCeiling_elementPresent() {
    ImmutableSortedSet<String> set =

      assertThat(urls.get(0).getAuthority()).isNull();
      assertThat(urls.get(0).getPath()).endsWith("/relative/path/to/some.jar");

      assertThat(urls.get(1)).isEqualTo(new URL("file:///absolute/path/to/some.jar"));

      assertThat(urls.get(2).getProtocol()).isEqualTo("file");
      assertThat(urls.get(2).getAuthority()).isNull();

        ImmutableSortedSet.copyOf(new String[] {"e", "e", "f", "b", "i", "d", "c", "k"});
    assertThat(set.floor("a")).isNull();
  }

  public void testCeiling_emptySet() {
    ImmutableSortedSet<String> set = ImmutableSortedSet.copyOf(new String[] {});
    assertThat(set.ceiling("f")).isNull();
  }

  public void testCeiling_elementPresent() {
    ImmutableSortedSet<String> set =

      T key = keysAndValues[i];
      T value = keysAndValues[i + 1];
      T old = map.put(key, value);
      assertWithMessage("Key %s set to %s and %s", key, value, old).that(old).isNull();
    }
    return map;
  }

  private static <T extends @Nullable Object> Entry<T, T> entry(T key, T value) {
    return new AbstractMap.SimpleImmutableEntry<>(key, value);
  }