public function testThisWeek()
 {
     $period = CarbonPeriod::thisWeek();
     $start = Carbon::today();
     $end = Carbon::tomorrow();
     if ($start->dayOfWeek !== Carbon::MONDAY) {
         $start->modify('last monday');
     }
     $this->assertEquals($start, $period->start());
     $this->assertEquals($end, $period->end());
 }