@Udf(description = "Returns the current number of milliseconds for the system since "
      + "1970-01-01 00:00:00 UTC/GMT.")
  public long unixTimestamp() {
    return System.currentTimeMillis();
  }
@Test
  public void shouldGetTheUnixTimestamp() {
    // Given:
    final long before = System.currentTimeMillis();

    // When:
    final long result = udf.unixTimestamp();
    final long after = System.currentTimeMillis();

    // Then:
    assertTrue(before <= result && result <= after);
  }