viewDidLeave not subscribable

[rob-moore]

Hey I'm working on getting tests up and running for a service that I wrote that uses the App in the constructor.

constructor(public appCtrl: App) {
		this.appCtrl.viewDidLeave.subscribe(view => {
			this.updateHistory(view);
		});
	}

Here's the constructor for the class that I'm testing and here is my test:

describe('tab service', () => {
	let tabSvc: TabService;
	let app: App;

	beforeEach(() => {
		app = AppMock.instance();

		TestBed.configureTestingModule({
			providers: [
				TabService,
			]
		});
		tabSvc = new TabService(app);
	});

	it('should have a updatehistoy method', () => {
		expect(tabSvc.updateHistory).toBe(true);
	});
});

Every time I run the test it seems like it gets to the constructor of my service then it fails with this error:

TypeError: this.appCtrl.viewDidLeave.subscribe is not a function

Any ideas on what's going on here? I looked at the code and it looks like viewDidLeave is available on your AppMock and should always be an Observable. Any idea why I can't subscribe to it?