If you have submitted an application form to an AFCO, you will routinely be called in for test. Depending on how busy the AFCO is, will depend on how long you wait for the letter calling you in to sit the Recruiting Test- timescales vary from two weeks to four on average. You can ring your AFCO direct to confirm your completed application form has been processed & to enquire when you are likely to be tested.
If you have not submitted an application form, but filled in an "Expression of Interest Form" it is forwarded to a central UK "Virtual AFCO" who will usually ring you in two or three weeks to see if you require further information, wish to attend a presentation, want to proceed with an application or are no longer interested.
In short, to get things moving, if you haven't already, submit a completed application form to your AFCO, then await a letter to invite you to sit the Recruiting Test.