docs: global beforeEach/beforeAll hooks

[yury-s]

Fixes #9468

[diegohaz]

This works, but TypeScript is completely clueless:

Am I right to assume this feature isn't supported yet?

[yury-s]

It is already supported. Looks like the type inference is busted without explicit template parameter, changing the declaration to

export const test = base.extend<{ forEachTest: void }>({
...

should resolve the problem. I'll update the docs.