assertThrows(
        UnsupportedOperationException.class,
        () -> map.entrySet().iterator().next().setValue("one"));
  }

  public void testTransformRemoveEntry() {
    Map<String, Integer> underlying = new HashMap<>();
    underlying.put("a", 1);
    Map<String, String> map = transformValues(underlying, Functions.toStringFunction());
    assertEquals("1", map.remove("a"));