Do you know if there's a way to use that runner per-file or per-project within jest? Seems like that's the only way it'd be possible to smoothly migrate in a large codebase without rewriting all tests at once.
You can define a base config for your repo, and then inherit two sub-configs from it each with different runners and mutually exclusive selection for tests (by suffix, folder, or any convention that works for you).
Glad that this one has the ability to be configured more granually - that'll come in handy for migrating gradually.