In the retryable reads spec, it notes that lowering the minHeartbetFrequencyMS can speed up the tests quite a bit, and the c driver actually does this for its tests. Unfortunately, another spec forbids drivers from allowing users (and therefore wrapping drivers) to modify this value.

The difference is pretty significant, though. For example, the retryable writes tests take about 40 seconds to run on my macbook with the default minHeartbeatFrequencyMS. With it set to 50, they take about 10 seconds.

Would it be possible to expose some undocumented way of lowering this value for wrapping drivers?