test/test/parallel/test-runner-concurrency.js

Node.js 18's node:test, as an npm package

// https://github.com/nodejs/node/blob/a3e110820ff98702e1761831e7beaf0f5f1f75e7/test/parallel/test-runner-concurrency.js

'use strict'
const common = require('../common')
const { describe, it, test } = require('#node:test')
const assert = require('assert')

describe('Concurrency option (boolean) = true ', { concurrency: true }, () => {
  let isFirstTestOver = false
  it('should start the first test', () => new Promise((resolve) => {
    setImmediate(() => { isFirstTestOver = true; resolve() })
  }))
  it('should start before the previous test ends', () => {
    // Should work even on single core CPUs
    assert.strictEqual(isFirstTestOver, false)
  })
})

describe(
  'Concurrency option (boolean) = false ',
  { concurrency: false },
  () => {
    let isFirstTestOver = false
    it('should start the first test', () => new Promise((resolve) => {
      setImmediate(() => { isFirstTestOver = true; resolve() })
    }))
    it('should start after the previous test ends', () => {
      assert.strictEqual(isFirstTestOver, true)
    })
  }
)

{
  // Make sure tests run in order when root concurrency is 1 (default)
  const tree = []
  const expectedTestTree = common.mustCall(() => {
    assert.deepStrictEqual(tree, [
      'suite 1', 'nested', 'suite 2',
      '1', '2', 'nested 1', 'nested 2',
      'test', 'test 1', 'test 2'
    ])
  })

  describe('suite 1', () => {
    tree.push('suite 1')
    it('1', () => tree.push('1'))
    it('2', () => tree.push('2'))

    describe('nested', () => {
      tree.push('nested')
      it('nested 1', () => tree.push('nested 1'))
      it('nested 2', () => tree.push('nested 2'))
    })
  })

  test('test', async (t) => {
    tree.push('test')
    await t.test('test1', () => tree.push('test 1'))
    await t.test('test 2', () => tree.push('test 2'))
  })

  describe('suite 2', () => {
    tree.push('suite 2')
    it('should run after other suites', expectedTestTree)
  })
}