Beta testing of models is usually straight forward stuff that does not require any real knowledge of aircraft design, etc. We leave the finer stuff like control surfaces and FDE to people that know their way around that and they concentrate there efforts on that.
Generally we are looking for people to simply use the AI and view it in the simulator as an AI on flight plans. Look at it from the tower position, from a chase plane and via the traffic board, etc. We are looking for anything that is out of place on the model as it goes through its lod and animation cycles. As an example, "I may have got the LOD 3 canopy animation wrong" instead of lifting in preflight, it stays down.
That is one example of what I am looking for and it will stand out to anybody that uses the model for a few hours.
Another examples may be, "you think the landing light is not operating correctly or there is strange object flying with the aircraft that you think is a bit weird".
Don't laugh, in FSX there are strange objects showing up in the exhaust trail
In the testing phase, we typically need a number of people to take the aircraft out of the hanger and fly it around at your favourite airport, as we understand that no one person is going to find all the faults, if a fault even exists.
Unlike beta testing of airport scenery, you only need to focus on one object as it goes through its operation and if you find nothing is wrong, that is fine but if you find something is wrong, then that makes for better model to enjoy.
It's fairly simple stuff, if you have eyes, then you can beta test.
Of course, we are also looking for people that can do it in timely manner as we wish to complete the model as soon as possible, not wait weeks for input to flow in before we can carry-on with the project. Sometimes there is no choice in this and can lead to a project going dead.