title: How can I test Paypal Express Checkout integration?
body: <p>I want to write unit test to test my Paypal Express Checkout integration. </p>
  
  <p>I have problem in the step where buyer authorize payment in Paypal screen</p>
  
  <p><img src="https://i.stack.imgur.com/mcUs0.jpg" alt="enter image description here"></p>
  
  <p>Is there a way to simulate this action in my test code?</p>
  
  <p>I use sandbox test account</p>