@Udf(description = "Converts a number of days since epoch to a DATE value.")
  public Date fromDays(final int days) {
    return new Date(TimeUnit.DAYS.toMillis(days));
  }
@Test
  public void shouldConvertToTimestamp() {
    assertThat(udf.fromDays(50), is(new Date(4320000000L)));
    assertThat(udf.fromDays(-50), is(new Date(-4320000000L)));
  }