chore(observeOn): fix skipped test

Closes ReactiveX#2457 ReactiveX#2459

spec/operators/observeOn-spec.ts

@@ -83,7 +83,7 @@ describe('observeOn operator', () => {
     expectSubscriptions(e1.subscriptions).toBe(sub);
   });
 
-  xit('should clean up subscriptions created by async scheduling (prevent memory leaks #2244)', (done) => {
+  it('should clean up subscriptions created by async scheduling (prevent memory leaks #2244)', (done) => {
     //HACK: Deep introspection to make sure we're cleaning up notifications in scheduling.
     // as the architecture changes, this test may become brittle.
     const results: number[] = [];
@@ -104,7 +104,7 @@ describe('observeOn operator', () => {
       .subscribe(
         x => {
           const observeOnSubscriber = subscription._subscriptions[0];
-          expect(observeOnSubscriber._subscriptions.length).to.equal(2); // 1 for the consumer, and one for the notification
+          expect(observeOnSubscriber._subscriptions.length).to.equal(2); // one for the consumer, and one for the notification
           expect(observeOnSubscriber._subscriptions[1].state.notification.kind)
             .to.equal('N');
           expect(observeOnSubscriber._subscriptions[1].state.notification.value)
@@ -114,10 +114,11 @@ describe('observeOn operator', () => {
         err => done(err),
         () => {
           // now that the last nexted value is done, there should only be a complete notification scheduled
+          // the consumer will have been unsubscribed via Subscriber#_parentSubscription
           const observeOnSubscriber = subscription._subscriptions[0];
-          expect(observeOnSubscriber._subscriptions.length).to.equal(2); // 1 for the consumer, one for the complete notification
+          expect(observeOnSubscriber._subscriptions.length).to.equal(1); // one for the complete notification
           // only this completion notification should remain.
-          expect(observeOnSubscriber._subscriptions[1].state.notification.kind)
+          expect(observeOnSubscriber._subscriptions[0].state.notification.kind)
             .to.equal('C');
           // After completion, the entire _subscriptions list is nulled out anyhow, so we can't test much further than this.
           expect(results).to.deep.equal([1, 2, 3]);