Simple test for Web Locks API

Refs: #416

test/locks.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const { isMainThread } = require('worker_threads');
+const { locks } = require('..');
+const { Thread } = locks;
+const metatests = require('metatests');
+
+const sleep = msec =>
+  new Promise(resolve => {
+    setTimeout(resolve, msec);
+  });
+
+if (isMainThread) {
+  metatests.test('locks: enter and leave', test => {
+    new Thread();
+    new Thread();
+
+    setTimeout(() => {
+      locks.request('A', async lock => {
+        test.end();
+      });
+    }, 100);
+  });
+} else {
+  locks.request('A', async lock => {
+    await sleep(100);
+  });
+}