@Udf
  public String uuid() {
    return java.util.UUID.randomUUID().toString();
  }
@Test
  public void shouldHaveCorrectOutputFormat() {
    // aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee
    final String anUuid = udf.uuid();
    assertThat(anUuid.length(), is(36));
    assertThat(anUuid.charAt(8), is('-'));
    assertThat(anUuid.charAt(13), is('-'));
    assertThat(anUuid.charAt(18), is('-'));
    assertThat(anUuid.charAt(23), is('-'));
    for (final char c : anUuid.toCharArray()) {
      assertThat(c, isIn(Arrays.asList('a', 'b', 'c', 'd', 'e', 'f', '1', '2', '3', '4', '5', '6',
          '7', '8', '9', '0', '-')));
    }
  }