I do not know if this suggestion has been mentioned elsewhere (the search function of the firum returned nothing), but I was wondering is an offline mode is / would be possible.
Nothing where one could submit his code (of course) but somewhere to have the possibility to compile the code and where the inputs of all test cases are given and which returns if the test is validated.
I thought since a lot of challenge give the content of the input for the expected output for all challenges, it would not be such an issue
In thise cases there is always to put both in a text file and compare at the beginning / the end of the execution, but its extra work that might only make sense in the more advanced challenges