How to get verification code for facebook test user

Question

My Facebook Login flow goes in several steps:

1. User is redirected to authorization url:

   https://www.facebook.com/dialog/oauth/?client_id={...}&redirect_uri={...}&scope={...}&state={...}

2. After user authentication I get verification code ( code field in facebook request)

3. I use the code parameter to get access token in request like this:

   https://graph.facebook.com/oauth/access_token?client_id={...}&client_secret={...}&redirect_uri={...}&code={...}

I want to write an automated test for my Facebook Login flow using Facebook test user. But for this I need to get the code parameter.

How can I get the code parameter for Facebook test user just like it is done for real user login?

Really waiting for your help!