feat: add support for boolean values for concurrency option

PR-URL: nodejs/node#43887
Fixes: nodejs/node#43837
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Jacob Smith <jacob@frende.me>
(cherry picked from commit dab492f0444b0a6ae8a41dd1d9605e036c363655)

README.md

@@ -328,9 +328,14 @@ internally.
   does not have a name.
 - `options` {Object} Configuration options for the test. The following
   properties are supported:
-  - `concurrency` {number} The number of tests that can be run at the same time.
+  - `concurrency` {number|boolean} If a number is provided,
+    then that many tests would run in parallel.
+    If truthy, it would run (number of cpu cores - 1)
+    tests in parallel.
+    For subtests, it will be `Infinity` tests in parallel.
+    If falsy, it would only run one test at a time.
     If unspecified, subtests inherit this value from their parent.
-    **Default:** `1`.
+    **Default:** `false`.
   - `only` {boolean} If truthy, and the test context is configured to run
     `only` tests, then this test will be run. Otherwise, the test is skipped.
     **Default:** `false`.

lib/internal/per_context/primordials.js

@@ -17,6 +17,7 @@ exports.Error = Error
 exports.ErrorCaptureStackTrace = (...args) => Error.captureStackTrace(...args)
 exports.FunctionPrototype = Function.prototype
 exports.FunctionPrototypeBind = (fn, obj, ...args) => fn.bind(obj, ...args)
+exports.MathMax = (...args) => Math.max(...args)
 exports.Number = Number
 exports.ObjectCreate = obj => Object.create(obj)
 exports.ObjectDefineProperties = (obj, props) => Object.defineProperties(obj, props)

lib/internal/test_runner/test.js

@@ -1,4 +1,4 @@
-// https://github.com/nodejs/node/blob/d83446b4c4694322e12d2b7d22592f2be674e580/lib/internal/test_runner/test.js
+// https://github.com/nodejs/node/blob/dab492f0444b0a6ae8a41dd1d9605e036c363655/lib/internal/test_runner/test.js
 
 'use strict'
 
@@ -7,6 +7,7 @@ const {
   ArrayPrototypeShift,
   ArrayPrototypeUnshift,
   FunctionPrototype,
+  MathMax,
   Number,
   PromisePrototypeThen,
   PromiseResolve,
@@ -55,8 +56,7 @@ const noop = FunctionPrototype
 const isTestRunner = getOptionValue('--test')
 const testOnlyFlag = !isTestRunner && getOptionValue('--test-only')
 // TODO(cjihrig): Use uv_available_parallelism() once it lands.
-const rootConcurrency = isTestRunner ? cpus().length : 1
-
+const rootConcurrency = isTestRunner ? MathMax(cpus().length - 1, 1) : 1
 const kShouldAbort = Symbol('kShouldAbort')
 
 function stopTest (timeout, signal) {
@@ -154,6 +154,12 @@ class Test extends AsyncResource {
 
     if (isUint32(concurrency) && concurrency !== 0) {
       this.concurrency = concurrency
+    } else if (typeof concurrency === 'boolean') {
+      if (concurrency) {
+        this.concurrency = isTestRunner ? MathMax(cpus().length - 1, 1) : Infinity
+      } else {
+        this.concurrency = 1
+      }
     }
 
     if (timeout != null && timeout !== Infinity) {

test/parallel/test-runner-concurrency.js

@@ -0,0 +1,31 @@
+// https://github.com/nodejs/node/blob/dab492f0444b0a6ae8a41dd1d9605e036c363655/test/parallel/test-runner-concurrency.js
+
+'use strict'
+require('../common')
+const { describe, it } = 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)
+    })
+  }
+)