That's tricky. There are lot of theories about Analytics, Chrome, AI, RNN, etc. Of course there also lot of speculations too!
BUT here Josh Bachynski explain that task completion is correlated with with user metrics - time on session, bounce rate and average pages per session. Also others - please note subsequent search in mine prev answer. So in theory sites with better time, less bounce are considered as high quality. You can check also other videos from Josh in YouTube where he explain this many times.
One of easiest way to track task completion is to add goals in Analytics and/or add events tracking too. Goals can be different - contact form filled, lead form filled, software download, whitepaper request, signup form, playing video, etc. Events can be - comments viewed, gallery viewed, video stopped, etc.Then you can see how many of your visitors do tasks and how many do events. This will be for your own insurance that they're inside of page and do something there.
Trick is that Google will use only SERP visitors and their metrics. I can have site with 20k visitors daily from Facebook/Twitter and only 200 from Google SERP. I don't saying that 20k visitors can be wrong, but they will be almost useless for clicking test. Things will be different if we have 20k daily from SERP and 200 from Facebook/Twitter.
So - whatever you do just when you receive SERP traffic keep it in site. This is higher priority for better ranking.