Perhaps jest.concurrent can be supported?

[liuxingbaoyu]

In the babel repository, it takes 42 seconds to run all tests locally (12 workers), and 35 seconds for babel-cli alone.

Because of the large number of subprocess operations involved, serial is very slow.

Perhaps we can make testing faster by supporting concurrency, greatly improving our local development experience.

I'm willing to try to implement this feature (probably not soon) and open this issue for your opinion.😃