test: add shareReplay firehose-source test (#6376)

spec/operators/shareReplay-spec.ts

@@ -347,6 +347,24 @@ describe('shareReplay', () => {
     });
   });
 
+  it('should stop listening to a synchronous observable when unsubscribed', () => {
+    const sideEffects: number[] = [];
+    const synchronousObservable = new Observable<number>((subscriber) => {
+      // This will check to see if the subscriber was closed on each loop
+      // when the unsubscribe hits (from the `take`), it should be closed
+      for (let i = 0; !subscriber.closed && i < 10; i++) {
+        sideEffects.push(i);
+        subscriber.next(i);
+      }
+    });
+
+    synchronousObservable.pipe(shareReplay({ refCount: true }), take(3)).subscribe(() => {
+      /* noop */
+    });
+
+    expect(sideEffects).to.deep.equal([0, 1, 2]);
+  });
+
   const FinalizationRegistry = (global as any).FinalizationRegistry;
   if (FinalizationRegistry) {
     it('should not leak the subscriber for sync sources', (done) => {