Why Take The Passengers On A Test Flight?
It seems that :-
The aircraft had returned to the gate because of technical trouble - (insufficient power?).
A repair had been carried out (hastily?).
The repair had been signed off - (presumably?)
...What I can't understand is why the passengers were aboard when the aircraft was subsequently cleared to fly on what was essentially a test flight.
This wasn't a case of an airliner suffering some trifling technical problem in some remote location and having to be repaired in the field this was Madrid for heaven's sake!
I doubt if this airline will survive this crash - and I'm sure all airlines will surely have to revise their procedures and, after any repairs, test fly all their aircraft empty before being cleared to embark passengers again.