In the Knapsack problem in the scheme track Knapsack in Scheme on Exercism using basic recursion will time out on the last test case even though the solution is correct. I would suggest either eliminating the last test case, or specify that the solution should scale sub-exponentially with number of items (or something to that extent).
The Exercism platform gives test runner something like 10 seconds to run before it kills them, so single test runs don’t cost the platform too much money.
The solution can scale any way you want. However, if you want the online test runner to mark tests as passed, you need to beat the timeout. This exercise is one of the few where that timeout window comes into play, which makes this one of the few optimization exercises.
It would be helpful to clarify this so people don’t spend time on a solution that will be rejected due to the timer, or simply remove the last test case.