I feel like there might be better ways of achieving the same, or similar, outcome. Using tax incentives for parents who take classes, teaching communication and psychology earlier in school, and improving social supports for families are some alternative ideas. A test has too many potential ways to go awry. Presumably, wealthy people could get tutors while economically disadvantaged parents might find paying for the test burdensome. Administration and bureaucracy around it might become unwieldy.

Also, passing a test doesn't mean you will be good at parenting. There are a lot of bad drivers out there that passed the test, doctors committing malpractice who passed exams, etc. I think the real difficulty would be in where the dividing line gets drawn between what is and isn't considered a good parent or ideal parenting style. The extremes are easy to identify, but the dividing line is not so clear.

In my experience, there are many parents who would like guidance on how to be better, and there are others who are not open to the idea of people suggesting ways for them to improve. To access the first group, just make help available and let them know about it. To impact in the second group would likely require a different intervention than an exam to be most effective. Often, people who are good parents had good parents, have robust social and economical supports, or had bad parents and are highly motivated to not repeat what was done to them. Strategies that factor these considerations might be more effective.

Also, parenting is important, but there have been studies that suggest that genetics and friends actually have more impact on how a person turns out than how their parents raised them. Nurture is very important. I'm not discounting it. I am all for educating parents. It is just one piece of the puzzle, though.

Plus, what would you do in cases where people didn't pass the test? How would you keep them from having kids anyway? That is a road that does not go to good places.