public function testHowToGetPreviousNextDate()
{
$jan1 = new Date(2013, 1, 1);
$dec31 = $jan1->previous();
$jan2 = $jan1->next();
$this->assertEquals(new Date(2012, 12, 31), $dec31);
$this->assertEquals(new Date(2013, 1, 2), $jan2);
}
