Respect --maxWorkers (nicolo-ribaudo#10)

README.md

@@ -13,8 +13,8 @@ The lists below are not comprehensive: feel free to [start a discussion](https:/
 - Jest globals: `expect`, `test`, `it`, `describe`, `beforeAll`, `afterAll`, `beforeEach`, `afterEach`
 - Jest function mocks: `jest.fn`, `jest.spyOn`
 - Inline and external snapshots
-- `--testNamePattern`/`-t`, to only run some specific tests
-- Jest config options: `setupFiles`, `snapshotSerializers`
+- Jest cli options: `--testNamePattern`/`-t`, `--maxWorkers`
+- Jest config options: `setupFiles`, `snapshotSerializers`, `maxWorkers`
 
 ### Unsupported Jest features
 

src/index.js

@@ -1,26 +1,26 @@
 import { Piscina } from "piscina";
 import supportsColor from "supports-color";
 import { MessageChannel } from "worker_threads";
-import os from "os";
 
 /** @typedef {import("@jest/test-result").Test} Test */
 
-const piscina = new Piscina({
-  filename: new URL("./worker-runner.js", import.meta.url).href,
-  maxThreads: os.cpus().length / 2,
-  env: {
-    // Workers don't have a tty; we whant them to inherit
-    // the color support level from the main thread.
-    FORCE_COLOR: supportsColor.stdout.level,
-    ...process.env,
-  },
-});
-
 export default class LightRunner {
   #config;
+  #piscina;
 
   constructor(config) {
     this.#config = config;
+
+    this.#piscina = new Piscina({
+      filename: new URL("./worker-runner.js", import.meta.url).href,
+      maxThreads: this.#config.maxWorkers,
+      env: {
+        // Workers don't have a tty; we whant them to inherit
+        // the color support level from the main thread.
+        FORCE_COLOR: supportsColor.stdout.level,
+        ...process.env,
+      },
+    });
   }
 
   /**
@@ -39,7 +39,7 @@ export default class LightRunner {
         mc.port2.onmessage = () => onStart(test);
         mc.port2.unref();
 
-        return piscina
+        return this.#piscina
           .run(
             { test, updateSnapshot, testNamePattern, port: mc.port1 },
             { transferList: [mc.port1] }