I was wondering and have looked about for a potential solution to our build becoming increasingly long based on how slow our Jest tests are becoming. In the grand scheme of things to run all of our test takes on average around 22-24 mins depending on the load across all of our VMs.
What I was looking for was a way to only run the test in the changed files relating to the PR in question. I wasn't and currently am unsure if this is possible. I have seen locally you can do so by running against all untracked files but that's not really an option once it's being tested on the servers.