WC_Order::set_date_completed PHP Method

    public function set_date_completed($timestamp)
    {
        $this->set_prop('date_completed', is_numeric($timestamp) ? $timestamp : strtotime($timestamp));
    }

 /**
  * Test: get_date_completed
  */
 function test_get_date_completed()
 {
     $object = new WC_Order();
     $object->set_date_completed('2016-12-12');
     $this->assertEquals('1481500800', $object->get_date_completed());
     $object->set_date_completed('1481500800');
     $this->assertEquals(1481500800, $object->get_date_completed());
 }