If statment inside cypress.io test

I'm new to testing and to cypress.io in particular, and I'm trying to test the registering flow in my app.

I want to check two scenarios -

1. If the user is trying to register with an existsting username, an error message is popping up.
2. Else - If proper inputs are inserted, the username is successfully registering.

How can I do so in one test ? there is an option to use if statement with cypress ?

Thanks a lot in advance.