Description

• Closes maxConcurrency no longer bounds in-flight tests in describe.concurrent, causing per-test resource leaks (regression from v3?) #10097
• Closes Reporting regression in V4: incorrect per-test duration with concurrent #10069
• Closes fix(runner): use per-group limiter for DFS-bounded concurrent scheduling #10108 (supersedes)

In #9653, we've changed concurrency limit from per-runTest level to per-indivisual user callbacks. While it sounds clean in principle, it lost runTest level serialization between siblings.

For example, with the following tests and maxConcurrent = 1:

beforeEach(async ({ task }) => {
  console.log("!> beforeEach", task.name)
  await sleep(10)
  console.log("!> beforeEach", task.name)
})

afterEach(async ({ task }) => {
  console.log("!> afterEach", task.name)
})

test.concurrent.for(["a", "b"])("%s", (_, { task }) => {
  console.log("!> test", task.name)
  await sleep(10)
  console.log("!< test", task.name)
})

before #9653:

!> beforeEach a
!< beforeEach a
!> test a
!< test a
!> afterEach a
!< afterEach a
!> beforeEach b
!< beforeEach b
!> test b
!< test b
!> afterEach b
!< afterEach b

and current main after #9653:

(Notably this still guarantees each callback level in-out concurrency limit but not beforeEach -> test -> afterEach lifecycle level in-out)

!> beforeEach a
!< beforeEach a
!> beforeEach b
!< beforeEach b
!> test a
!< test a
!> test b
!< test b
!> afterEach a
!< afterEach a
!> afterEach b
!< afterEach b

This PR brings back siblings serialization guarantee by introducing independent concurrency limit at each task branch. This now also guarantees sibling suite hooks concurrency guarantee which has never existed even before #9653.

TODO

• summary
• test

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