@Udf
  public String uuid() {
    return java.util.UUID.randomUUID().toString();
  }
@Test
  public void shouldReturnDistinctValueEachInvocation() {
    int capacity = 1000;
    final Set<String> outputs = new HashSet<String>(capacity);
    for (int i = 0; i < capacity; i++) {
      outputs.add(udf.uuid());
    }
    assertThat(outputs, hasSize(capacity));
  }