public void test_minus_Period_negativeDays() {

    MockSimplePeriod period = MockSimplePeriod.of(-25, ChronoUnit.DAYS);
    LocalDateTime t = this.TEST_2007_07_15_12_30_40_987654321.minus(period);
    assertEquals(t, LocalDateTime.of(2007, 8, 9, 12, 30, 40, 987654321));
  }

  @Test(expectedExceptions = NullPointerException.class, groups = { "tck" }