@Udf
  public String uuid() {
    return java.util.UUID.randomUUID().toString();
  }
@Test
  public void shouldReturnCorrectOutputFormat() {
    // aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee
    final String anUuid = udf.uuid();

    final java.util.UUID uuid = java.util.UUID.fromString(anUuid);
    final ByteBuffer bytes = ByteBuffer.wrap(new byte[16]);
    bytes.putLong(uuid.getMostSignificantBits());
    bytes.putLong(uuid.getLeastSignificantBits());
    byte[] byteArrays = bytes.array();

    final String toUuid = udf.uuid(ByteBuffer.wrap(byteArrays));
    assertThat(toUuid, is(anUuid));
  }