Ember Mirage - Assertion Failed: `actions` must be provided at extend time, not at create time

Good day,

I’m in the middle of upgrading our Ember app (from v. 1.13.15 to v. 2.4.2). Also, we have Mirage setup for our testing. When running ember server --test, I get the following errors:

Error: Assertion Failed: actions must be provided at extend time, not at create time, when Ember.ActionHandler is used (i.e. views, controllers & routes).

Anyone, has an idea what this means?

P.S. I attached an image of the error: