I might be missing something, but k6 should be able to completely cover all of your use cases? I am one of the k6 developers, can you share exactly what the missing piece was?
> tests that would run much much more often (like every seconds or couple of seconds), in a continuous manner.
You can do that, just use an arrival-rate executor that runs an iteration every second, with a test duration of 365 days or something like that :) See https://k6.io/docs/using-k6/scenarios/arrival-rate
> Tue goal was to have something at the same time like a healtcheck (is it still working), like a performance test (does it answer in a timely manner) and like a validation test (does it answer the right result - the endpoints we wanted to test do "complex calculations"). Our best answer so far was to wrap K6 in an infinite loop, but I wonder if there could be something smarter.
You can certainly wrap k6 in an infinite loop. Nothing wrong with that, though you can probably use the `scenarios` feature (with long `duration` values) to achieve it without wrapping k6: https://k6.io/docs/using-k6/scenarios
> tests that would run much much more often (like every seconds or couple of seconds), in a continuous manner.
You can do that, just use an arrival-rate executor that runs an iteration every second, with a test duration of 365 days or something like that :) See https://k6.io/docs/using-k6/scenarios/arrival-rate
> Tue goal was to have something at the same time like a healtcheck (is it still working), like a performance test (does it answer in a timely manner) and like a validation test (does it answer the right result - the endpoints we wanted to test do "complex calculations"). Our best answer so far was to wrap K6 in an infinite loop, but I wonder if there could be something smarter.
You can certainly wrap k6 in an infinite loop. Nothing wrong with that, though you can probably use the `scenarios` feature (with long `duration` values) to achieve it without wrapping k6: https://k6.io/docs/using-k6/scenarios