Dependecy Injection

gistfile1.rb

class Payment
  def process(gateway)
    gateway.verify(self) # duck typed.
  end
end

class PaymentTest
  def test_process
    payment = Payment.new
    payment.process(MockGatway.new)
  end
end

# in the real code

gateway = AuthNet::Gateway.new # Stripe, Braintree, etc.
payment.process(gateway)