test(switch): should not leak ChildSubscriptions (ReactiveX#2355)

spec/operators/switch-spec.ts

@@ -223,4 +223,44 @@ describe('Observable.prototype.switch', () => {
 
     expect(completed).to.be.true;
   });
-});
+
+  it('should not leak when child completes before each switch', () => {
+    let iStream: Rx.Subject<number>;
+    const oStreamControl = new Rx.Subject<number>();
+    const oStream = oStreamControl.map(() => {
+      return (iStream = new Rx.Subject());
+    });
+    const switcher = oStream.switch();
+    const result = [];
+    let sub = switcher.subscribe((x: number) => result.push(x));
+
+    [0, 1, 2, 3, 4].forEach((n) => {
+      oStreamControl.next(n); // creates inner
+      iStream.complete();
+    });
+    // Expect one child of switch(): The oStream
+    expect(
+      (<any>sub)._subscriptions[0]._innerSub._subscriptions.length
+    ).to.equal(1);
+    sub.unsubscribe();
+  });
+
+  it('should not leak if we switch before child completes', () => {
+    const oStreamControl = new Rx.Subject<number>();
+    const oStream = oStreamControl.map(() => {
+      return (new Rx.Subject());
+    });
+    const switcher = oStream.switch();
+    const result = [];
+    let sub = switcher.subscribe((x: number) => result.push(x));
+
+    [0, 1, 2, 3, 4].forEach((n) => {
+      oStreamControl.next(n); // creates inner
+    });
+    // Expect two children of switch(): The oStream and the first inner
+    expect(
+      (<any>sub)._subscriptions[0]._innerSub._subscriptions.length
+    ).to.equal(2);
+    sub.unsubscribe();
+  });
+});