the devs at factorio have developed an amazing test suite automation system to automate regression tests. I wouldnt be surprised if this is what gives them most of their confidence to do twice daily releases. I thought it was newer, but they seem to have had it for the past 6 years. So i guess my point is they dont need to 100% trust every dev (while I'm sure they could with such a small team) they can instead trust in the tests.
https://www.factorio.com/blog/post/fff-62 https://www.factorio.com/blog/post/fff-186