It's really hard to believe that in today's day and age they cannot do adequate testing to determine the affects on these devices on a plane's controls. ...
It's very hard to standardize testing since there are so many variables that could pop up at some point.
For example, there are literally miles and miles of wiring and cabling throughout the aircraft. Over time, many of the harnesses and shrouds might thin out, crack or even get chewed on by pests - when the wires inside are exposed, they may become more sensitive to stray RF.
Airbus aircraft rely more on computers and electronic signalling for flight controls, so their designs might be more sensitive to potential problems if wiring protection is compromised.
So there is no real hard and fast test to declare all aircraft are safe since the conditions that might potentially cause a problem are variable.