fix(NODE-6151): MongoClient connect does not keep Node.js running (#4101)

Author: W-A-James

src/timeout.ts

@@ -41,7 +41,7 @@ export class Timeout extends Promise<never> {
   public timedOut = false;
 
   /** Create a new timeout that expires in `duration` ms */
-  private constructor(executor: Executor = () => null, duration: number) {
+  private constructor(executor: Executor = () => null, duration: number, unref = false) {
     let reject!: Reject;
 
     if (duration < 0) {
@@ -63,8 +63,8 @@ export class Timeout extends Promise<never> {
         this.timedOut = true;
         reject(new TimeoutError(`Expired after ${duration}ms`));
       }, this.duration);
-      // Ensure we do not keep the Node.js event loop running
-      if (typeof this.id.unref === 'function') {
+      if (typeof this.id.unref === 'function' && unref) {
+        // Ensure we do not keep the Node.js event loop running
         this.id.unref();
       }
     }
@@ -78,8 +78,8 @@ export class Timeout extends Promise<never> {
     this.id = undefined;
   }
 
-  public static expires(durationMS: number): Timeout {
-    return new Timeout(undefined, durationMS);
+  public static expires(durationMS: number, unref?: boolean): Timeout {
+    return new Timeout(undefined, durationMS, unref);
   }
 
   static is(timeout: unknown): timeout is Timeout {

test/unit/timeout.test.ts

@@ -23,12 +23,12 @@ describe('Timeout', function () {
       beforeEach(() => {
         timeout = Timeout.expires(2000);
       });
-      it('creates a timeout instance that will not keep the Node.js event loop active', function () {
+      it.skip('creates a timeout instance that will not keep the Node.js event loop active', function () {
         expect(timeout).to.have.property('id');
         // @ts-expect-error: accessing private property
         const id = timeout.id;
         expect(id?.hasRef()).to.be.false;
-      });
+      }).skipReason = 'Skipping until further work during CSOT implementation';
       it('throws a TimeoutError when it expires', async function () {
         try {
           await timeout;