public virtual void test_subtractFrom()
 {
     assertEquals(P1D.subtractFrom(LocalDate.of(2014, 6, 30)), LocalDate.of(2014, 6, 29));
     assertEquals(P1W.subtractFrom(OffsetDateTime.of(2014, 6, 30, 0, 0, 0, 0, ZoneOffset.UTC)), OffsetDateTime.of(2014, 6, 23, 0, 0, 0, 0, ZoneOffset.UTC));
 }
 //-------------------------------------------------------------------------
 public virtual void test_addTo()
 {
     assertEquals(P1D.addTo(LocalDate.of(2014, 6, 30)), LocalDate.of(2014, 7, 1));
     assertEquals(P1W.addTo(OffsetDateTime.of(2014, 6, 30, 0, 0, 0, 0, ZoneOffset.UTC)), OffsetDateTime.of(2014, 7, 7, 0, 0, 0, 0, ZoneOffset.UTC));
 }