public function testSetRate()
 {
     $this->specify('sets the rate', function () {
         $i = new \CoinSimple\Invoice();
         verify($i->data())->equals(array());
         $i->setRate('coinsimple');
         $data = $i->data();
         verify(array_key_exists('rate', $data))->true();
         verify($data['rate'])->equals("coinsimple");
     });
     $this->specify('converts the rate to lowercase', function () {
         $i = new \CoinSimple\Invoice();
         verify($i->data())->equals(array());
         $i->setRate('CoinSimple');
         $data = $i->data();
         verify(array_key_exists('rate', $data))->true();
         verify($data['rate'])->equals("coinsimple");
     });
 }