It sounds like a throwaway side project where he/she has to practically apply the skillset they want to cultivate would be a more useful experience than hitting

It sounds like a throwaway side project where he/she has to practically apply the skillset they want to cultivate would be a more useful experience than hitting the textbooks, which is how I interpreted their last comment. It could also be useful to have even a relatively shallow body of work to demonstrate some degree of competency, given they've not been doing it commercially to date and like every right-thinking individual, doesn't enjoy algorithm-orientated tests! @OP - personally I wouldn't quit. Depending on your annual leave/worktime arrangements could you take 1 day a week off for the foreseeable future to pursue your career change? Alternatively could you migrate to (or even create) a more desirable role within your current employer in the meantime? If you can demonstrate a strong business case for it they might just facilitate your career change themselves...