Test razorpay payment flow using cypress

I am trying to use cypress[https://github.com/cypress-io/cypress] for testing my Razorpay payment flow in my ROR project.I am able to get fields in iframe,select a bank and click on "Pay rs399 now".On clicking the "Pay now button" a new window opens up which has two options to make the payment successfull OR fail it. Everything till now is already tested in cypress... My question is how do I access the new window opened using cypress and click "success"