Collection of information/links on code challenges that I have taken part in but cannot easily share code in my own github.
Euler project is a large collection of small scale coding challenges that anyone can do. Because Euler project explicitly forbids sharing code solutions to their challenges, unfortunately I can only provide proof of my coding on request basis. So far, I have done around first 40 challenges using c++ in my private repository but this can change in the future if I find the motivation to do so.
CodeCrafters provides semi step-by-step guides/challenges on different coding topics. All their challenges contain automated tests which support multiple coding languages. While on default, all the challenges cost real money to use, they do provide monthly free to use windows on one or two of them at any given time.
I have so far taken part in 5 of them while they have been free to use and my up-to-date progress can be found here. Technically CodeCrafters doesn't forbid anyone from sharing their code solutions. However, because of how their testing system works in the challenges, it would be inconvinient to push code into own github. Basically, I can share solutions on request.