We do coding tests of course but that would be too limited on its own.
Personally, I would be not where I am without college and ton of courses in CS. Topics like Database normalization, query optimization, ton of OS concepts, discrete math, algorithms/data structures are important for any CS career and could be read on their own but why not just take courses and study them in college instead of trying to rely one's self discipline to cover all of that.
If you are starting your own company, maybe it matters less but even there I am not sure.