original.put(SomeEnum.SOME_INSTANCE, 0);
    EnumMap<SomeEnum, Integer> copy = Maps.newEnumMap(original);
    assertEquals(original, copy);
  }

  public void testEnumMapWithInitialEmptyMap() {
    Map<SomeEnum, Integer> original = new HashMap<>();
    assertThrows(IllegalArgumentException.class, () -> Maps.newEnumMap(original));
  }