Excellent; many thanks for the detailed and informative response 
Edit:
A couple of further questions, if I may:
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On Hackerrank, the Author can access a (private) simulated view of the Problem, and so submit solutions and time how long it takes on Codechef’s servers, etc, and also see exactly how it will be rendered when viewed by a contestant - is that kind of thing available here?
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Hackerrank also has a rigid set of rules regarding the naming of test input files and of output files. Is Codechef the same, or is it more free-form? Does this naming scheme (if any) including which subtask the test input belongs to (or maybe there is a folder for each subtask and the relevant input files go inside it)?