public void ShouldProduceValidReceiptWhenBuying(int[] coins, int minutes)
        {
            foreach (var coin in coins)
            {
                _ps.AddPayment(coin);
            }
            IReceipt receipt = _ps.Buy();

            Assert.That(receipt, Is.Not.Null);
            Assert.That(receipt.Value(), Is.EqualTo(minutes));
        }
 public IReceipt Buy()
 {
     return(_payStation.Buy());
 }