Recurr\Rule::setWeekStart PHP Méthode

    public function setWeekStart($weekStart)
    {
        $weekStart = strtoupper($weekStart);
        if (!in_array($weekStart, array('MO', 'TU', 'WE', 'TH', 'FR', 'SA', 'SU'))) {
            throw new InvalidArgument('Week Start must be one of MO, TU, WE, TH, FR, SA, SU');
        }
        $this->weekStart = $weekStart;
        $this->weekStartDefined = true;
        return $this;
    }

 /**
  * @expectedException \Recurr\Exception\InvalidArgument
  */
 public function testBadWeekStart()
 {
     $this->rule->setWeekStart('monday');
 }