use isMainThread

Author: MoonBall

test/fixtures/es-modules/tla/unresolved-with-worker-process-exit.mjs

@@ -1,8 +1,6 @@
-import { Worker } from 'worker_threads';
+import { Worker, isMainThread } from 'worker_threads';
 
-// Do not use isMainThread so that this test itself can be run inside a Worker.
-if (!process.env.HAS_STARTED_WORKER) {
-  process.env.HAS_STARTED_WORKER = 1;
+if (isMainThread) {
   new Worker(new URL(import.meta.url));
   await new Promise(() => {});
 } else {