Car wont start even after having a machanic test and everything was in good working

I see a jump start was needed to get the engine started - that is indicative of a failing battery - failing alternator - parasitic load on battery when vehicle is parked or possibly a starter motor malfunction. Unfortunately it can be rather difficult to diagnose unless the problem is occurring at the time of testing.. The auto repair facility may need to keep the vehicle for a few days so further *hands-on* testing can be completed.