public void test_minusWeeks_symmetry(LocalDateTime reference) {

    for (int weeks = 0; weeks < 365 * 8; weeks++) {
      LocalDateTime t = reference.minusWeeks(weeks).minusWeeks(-weeks);
      assertEquals(t, reference);

      t = reference.minusWeeks(-weeks).minusWeeks(weeks);
      assertEquals(t, reference);
    }
  }

  @Test(groups = { "tck" }