There are now probably more people killed by police shootings than die in air crashes each year, and we insist that pilots get all kinds of simulator tests before they get to fly what can be killing machines. Why not similar testing for cops? Indeed, simulators do exist.
The real dilemma in these police shooter cases comes from the fact that the problem is not that white cops want to kill blacks, rather it is that their deeply ingrained and often unconscious racism makes it hard for them to make objectively correct split second decisions. Then, grand juries apply a subjective standard (did the cop really believe he was in danger), and then, because he did, there is no punishment, and much natural anger.
So the solution is that before a cop can be approved for patrol duty, they have to pass a simulator test in which they have to deal with varied situations that include both those that are objectively ones in which deadly force is justified, and those in which it is not, and of course with different racial configurations. That would mean that cop candidates can not pass by just never using deadly force, but rather that their ability to analyze and react quickly is properly tested. The result, particularly after proper training, would surely be better and more confident policing all around. There is research suggesting greater reluctance to shoot blacks, which would mean both that this is much more complicated that it might seem, and also that such testing might be successful at finding the minority for which this is not true.
Note: This post has been updated to reflect that such simulators are available, and that the research shows how complicated this is.