Others may know much more than me, but from my limited experience of Nigeria, I'd suggest fairly poor.
You have a capable air force, and also that air force has a very good undergraduate aeronautical engineering programme at Kaduna. Additionally, the NAF is now sending some of its best people to do MScs in aerospace engineering at Cranfield University in the UK - which provides a very good education that usually includes substantial flight test elements.
I don't know if the NAF is putting anybody through a Test Pilot School, but even without that, it seems likely to me that high experience ex-NAF people (possibly people who have split their careers between operational flying and engineering branches) are the most likely to get any local test flying jobs.
Add into that, that so far as I know the licence aircraft manufacture of RV-6 Air Beetles has ended, so there's unlikely to be much employment in that direction either.
Nonetheless, best of luck - you only need one job.