`best_priority()` tries to measure unmeasured and failing relays first. But if `fraction_relays` or `min_relays` always fail, those relays will always end up first in the priority queue. (More precisely, those relays will end up first in the priority queue, until the results of the good relays ~~time out~~ are discarded for being too old.) Thinking about starvation is complicated, because of the `freshness_reduction_factor` on some errors. Here's a very simple algorithm that avoids starving good relays for failed relays: 1. Count the number of times that sbws has attempted to get a result from each relay. 2. Test the relays with the lowest number of attempts first. (Don't check if the attempt succeeded or failed.) For this priority rule to work, every time a relay is queued, it must get a result. Here's how we can make that happen" * Modify `result_putter_error()` to store an error result to the queue. * Make sure timeouts store an error result to the queue. * Add a unit test and integration test that makes sure every queued relay has a result. Here's an alternative that might be simpler to implement: * before a relay is queued using `pool.apply_async()` in `run_speedtest()`, store a `ResultAttempt` to the queue * only count `ResultAttempt`s when prioritising relays