test: fix timeouts when running worker tests with --worker

These tests have been added after the original workers PR and
time out when run inside a worker by themselves.
This is needed for enabling `--worker` tests in our regular CI.
Refs: nodejs/build#1318
PR-URL: #21791
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Refael Ackermann <refack@gmail.com>

Author: addaleax

test/parallel/test-worker-exit-code.js

@@ -7,9 +7,11 @@ const common = require('../common');
 
 constassert=require('assert');
 constworker=require('worker_threads');
-const{ Worker,isMainThread,parentPort }=worker;
+const{ Worker, parentPort }=worker;
 
-if(isMainThread){
+// 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;
 parent();
 }else{
 if(!parentPort){

test/parallel/test-worker-onmessage.js

@@ -2,9 +2,11 @@
 'use strict';
 constcommon=require('../common');
 constassert=require('assert');
-const{ Worker,isMainThread,parentPort }=require('worker_threads');
+const{ Worker, parentPort }=require('worker_threads');
 
-if(isMainThread){
+// 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;
 constw=newWorker(__filename);
 w.on('message',common.mustCall((message)=>{
 assert.strictEqual(message,4);