feat: add maxConcurrency option

docs/config/index.md

@@ -533,3 +533,12 @@ Vitest will not fail, if no tests will be found.
 - **Default**: `false`
 
 Show heap usage after each test. Useful for debugging memory leaks.
+
+### maxConcurrency
+
+- **Type**: `number`
+- **Default**: `5`
+
+A number of tests that are allowed to run at the same time marked with `test.concurrent`.
+
+Test above this limit will be queued to run when available slot appears.

packages/vitest/package.json

@@ -119,6 +119,7 @@
     "micromatch": "^4.0.5",
     "mlly": "^0.5.2",
     "natural-compare": "^1.4.0",
+    "p-limit": "^4.0.0",
     "pathe": "^0.2.0",
     "picocolors": "^1.0.0",
     "pkg-types": "^0.3.2",

packages/vitest/src/defaults.ts

@@ -72,6 +72,7 @@ const config = {
   open: true,
   coverage: coverageConfigDefaults,
   fakeTimers: fakeTimersDefaults,
+  maxConcurrency: 5,
 }
 
 export const configDefaults: Required<Pick<UserConfig, keyof typeof config>> = Object.freeze(config)

packages/vitest/src/runtime/run.ts

@@ -1,3 +1,4 @@
+import limit from 'p-limit'
 import type { File, HookCleanupCallback, HookListener, ResolvedConfig, Suite, SuiteHooks, Task, TaskResult, TaskState, Test } from '../types'
 import { vi } from '../integrations/vi'
 import { getSnapshotClient } from '../integrations/snapshot/chai'
@@ -195,6 +196,8 @@ export async function runSuite(suite: Suite) {
 
   updateTask(suite)
 
+  const workerState = getWorkerState()
+
   if (suite.mode === 'skip') {
     suite.result.state = 'skip'
   }
@@ -207,7 +210,8 @@ export async function runSuite(suite: Suite) {
 
       for (const tasksGroup of partitionSuiteChildren(suite)) {
         if (tasksGroup[0].concurrent === true) {
-          await Promise.all(tasksGroup.map(c => runSuiteChild(c)))
+          const mutex = limit(workerState.config.maxConcurrency)
+          await Promise.all(tasksGroup.map(c => mutex(() => runSuiteChild(c))))
         }
         else {
           for (const c of tasksGroup)
@@ -225,8 +229,6 @@ export async function runSuite(suite: Suite) {
   }
   suite.result.duration = now() - start
 
-  const workerState = getWorkerState()
-
   if (workerState.config.logHeapUsage)
     suite.result.heap = process.memoryUsage().heapUsed
 

packages/vitest/src/types/config.ts

@@ -344,6 +344,12 @@ export interface InlineConfig {
    * Return `false` to ignore the log.
    */
   onConsoleLog?: (log: string, type: 'stdout' | 'stderr') => false | void
+
+  /**
+   * A number of tests that are allowed to run at the same time marked with `test.concurrent`.
+   * @default 5
+   */
+  maxConcurrency?: number
 }
 
 export interface UserConfig extends InlineConfig {