feat!(runner): support concurrent suites

[hi-ogawa]

Description

• closes concurrent.each executes iterations serially instead of concurrently #5458

PoC of running multiple suites concurrently.

In terms of implementation, it looks like it's a matter of setting Suite.concurrent = true in some way. My current approach is to have an explicit flag TestOptions.concurrentSuite: boolean and the idea is based on the analogy:

• describe("...", { concurrentSuite: true }, ...) to run neighboring suites concurrently
• test("...", { concurrent: true }, ...) to run neighboring tests concurrently

TBD

• comparison with Jest?
  • they runs all test.concurrent first whether it is inside describe and they have before/after hooks related bugs.
• breaking change? (change describe.concurrent to affect all suite/task level concurrency)
• limit concurrency only for tests but not for suites? otherwise, it's easy to make deadlock where outer concurrent describe is waiting for inner concurrent test to finish, then inner one is blocked by p-limit.

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. If the feature is substantial or introduces breaking changes without a discussion, PR might be closed.
• Ideally, include a test that fails without this PR but passes with it.
• Please, don't make changes to pnpm-lock.yaml unless you introduce a new test example.

Tests

• Run the tests with pnpm test:ci.

Documentation

• If you introduce new functionality, document it. You can run documentation with pnpm run docs command.

Changesets

• Changes in changelog are generated from PR name. Please, make sure that it explains your changes in an understandable manner. Please, prefix changeset messages with feat:, fix:, perf:, docs:, or chore:.

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[jgoux]

Hey @hi-ogawa, thanks for implementing it.

I'm wondering why "concurrentSuite" is needed? Shouldn't we mimic jest and have all the describe blocks concurrent? Or is it for backward compat only?

If people like me want jest behaviour on all describe blocks, could we add a concurrentSuite parameter in vitest.config.ts so it's enabled globally?

[hi-ogawa]

I'm wondering why "concurrentSuite" is needed? Shouldn't we mimic jest and have all the describe blocks concurrent? Or is it for backward compat only?

I think I was mostly concerned with back compat, but anyways this PR is just for a starting point of discussion to explore the idea. Depending on what users expect and how Jest has been doing, we'll discuss further what this feature should be.