public function isEqualTo($interval, $failMessage = null)
{
list($date1, $date2) = $this->getDates($interval);
if ($date1 == $date2) {
$this->pass();
} else {
$this->fail($failMessage ?: $this->_('Interval %s is not equal to %s', $this, $this->format($interval)));
}
return $this;
}