Iterable<String> iterable = asList("foo", "bar");
    assertThrows(IllegalArgumentException.class, () -> getOnlyElement(iterable, "x"));
  }

  @GwtIncompatible // Iterables.toArray(Iterable, Class)
  public void testToArrayEmpty() {
    Iterable<String> iterable = emptyList();
    String[] array = Iterables.toArray(iterable, String.class);
    assertTrue(Arrays.equals(new String[0], array));
  }