Fantastic read. My only concern is that there wasn't any talk around cost of false positives (selecting a test to run where it is unnecessary) vs false negatives (incorrectly dismissing a relevant test), as those costs in terms of their effect is not symmetrical.
The cost of a bug slipping through because a test being skipped will be higher than running an irrelevant test to a commit.
The cost of a bug slipping through because a test being skipped will be higher than running an irrelevant test to a commit.