The flight crew’s decision to conduct a post-maintenance stall test in an area of icing conditions, which resulted in wing contamination that significantly decreased the airplane’s critical angle of attack. Also causal was the airplane manufacturer’s lack of training and experience requirements for the flight crew to safely conduct the stall test, which resulted in an attempted remedial action that aggravated the aerodynamic stall and led to a loss of control from which they were unable to recover. Contributing to the accident was the flight crew’s failure to follow the test conditions regarding cloud clearance, altitude limit, visual meteorological conditions, and ensuring all external surfaces were free from ice.