test,worker: add more tests for worker.ref()/.unref()

PR-URL: https://github.com/nodejs/node/pull/26083
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-worker-ref-onexit.js

@@ -0,0 +1,10 @@
+'use strict';
+const common = require('../common');
+const { Worker } = require('worker_threads');
+
+// Check that worker.unref() makes the 'exit' event not be emitted, if it is
+// the only thing we would otherwise be waiting for.
+
+const w = new Worker('', { eval: true });
+w.unref();
+w.on('exit', common.mustNotCall());

test/parallel/test-worker-ref.js

@@ -0,0 +1,29 @@
+'use strict';
+const common = require('../common');
+const { Worker } = require('worker_threads');
+
+// Test that calling worker.unref() leads to 'beforeExit' being emitted, and
+// that we can resurrect the worker using worker.ref() from there.
+
+const w = new Worker(`
+const { parentPort } = require('worker_threads');
+parentPort.once('message', (msg) => {
+  parentPort.postMessage(msg);
+});
+`, { eval: true });
+
+process.once('beforeExit', common.mustCall(() => {
+  console.log('beforeExit');
+  w.ref();
+  w.postMessage({ hello: 'world' });
+}));
+
+w.once('message', common.mustCall((msg) => {
+  console.log('message', msg);
+}));
+
+w.on('exit', common.mustCall(() => {
+  console.log('exit');
+}));
+
+w.unref();