WordPress has always been recognized as a very welcoming platform for developers at any level of expertise. The block editor introduced in WordPress 5.0 release is not only an entirely new editing experience for users, but it also redefines the way plugins and themes are developed.
Simpler API, less boilerplate code.
Flexible and easy configuration.
Test files executed in isolation.
Advanced watch mode.
Snapshots support = easier start with testing.
Mocha has still a bit better performance (according to my quick tests).
My analysis got very positive feedback, with only a few little concerns, so I got encouraged to take action and verify the assumptions stated. I picked two different projects to play with to ensure both of them will uniformly benefit from using Jest.