Roul, you suggest that no stall tests were conducted for the accident configuration; you may be right.
This accident appears to have been beyond anything foreseen by both the manufacturer and regulator, yet with hindsight, imagination - stating the obvious, it is suddenly easy.
The lack of foresight probably involved similar mental processes as the crew's inability to comprehend the situation; the regulators had several years to think about this, the crew much less.
There is no guarantee that even the highest standard of aircraft certification or an exceptional crew will prevent all accidents. Aircraft certification and crew regulation depend on judgement of reasonably low risk; aircraft system failures use probability (e.g. 10-9), but human performance and training is much more subjective; these aspects include awareness and decision making.