Caching test results
Unison is capable of caching unit tests results (not integration tests). Once a unit test result is cached, no one else needs to run it again. They can achieve that because Unison is an FP language that tracks effects, and access to IO is not permitted in unit tests, so all unit tests need to be pure functions.
Arguably, there’s less developer churn bin Unison, since we won’t get incompatibilities between library versions, and it will always be possible to use more than one lib version at the same time. The reason for that is that different library versions don’t need to compete for names, because everything’s a unique SHA.