When\When::bymonth PHP Method

    public function bymonth($bymolist, $delimiter = ",")
    {
        if ($this->bymonths = self::prepareItemsList($bymolist, $delimiter, 'monthNum')) {
            return $this;
        }
        throw new \InvalidArgumentException("bymonth: Accepts values between 1 and 12");
    }

 /**
  * @expectedException InvalidArgumentException
  */
 public function testInvalidByMonth()
 {
     $test = new When();
     $test->bymonth(-1);
 }