public function testHowToAddRemoveADurationFromItInDays()
{
$jan1 = new Date(2013, 1, 1);
$dec31 = $jan1->minus(new Duration(1, TimeUnit::day()));
$jan3 = $jan1->plus(new Duration(2, TimeUnit::day()));
$this->assertEquals(new Date(2012, 12, 31), $dec31);
$this->assertEquals(new Date(2013, 1, 3), $jan3);
}
