How to unit test unsubscribe function in angular

Question

I would like to find a way to test unsubscribe function calls on Subscriptions and Subjects.

I came up with a few possible solutions, but every one of these have pros and cons. Please keep in mind that I do not want to alter the access modifier of a variable for testing purposes.

1. Accessing private variable of component with reflection.

In that case I have a private class variable which stores a subscription:

component.ts:

private mySubscription: Subscription;
//...
ngOnInit(): void {
    this.mySubscription = this.store
        .select(mySelector)
        .subscribe((value: any) => console.log(value));
}

ngOnDestroy(): void {
    this.mySubscription.unsubscribe();
}

---

component.spec.ts:

spyOn(component['mySubscription'], 'unsubscribe');
component.ngOnDestroy();
expect(component['mySubscription'].unsubscribe).toHaveBeenCalledTimes(1);

---

pros:

• I can reach mySubscription.
• I can test that the unsubscribe method was invoked on the right subscription.

cons:

• I can reach mySubscription only with reflection, what I would like to avoid if possible.

---

2. I create a variable for subscription just like in option 1., but instead of reaching the variable with reflection I simply check that the unsubscribe method was invoked, without knowing the source.

component.ts: same as in option 1

---

component.spec.ts:

spyOn(Subscription.prototype, 'unsubscribe');
component.ngOnDestroy();
expect(Subscription.prototype.unsubscribe).toHaveBeenCalledTimes(1);

---

pros:

• I can test that the unsubscribe method was called

cons:

• I can not test the source of the invoked unsubscribe method.

---

3. I implemented a helper function which invokes unsubscribe method on the passed parameters which are subscriptions.

subscription.helper.ts:

export class SubscriptionHelper {

    static unsubscribeAll(...subscriptions: Subscription[]) {
        subscriptions.forEach((subscription: Subscription) => {
                subscription.unsubscribe();
            });
    }
}

---

component.ts: same as in option 1, but ngOnDestroy is different:

ngOnDestroy(): void {
    SubscriptionHelper.unsubscribeAll(this.mySubscription);
}

---

component.spec.ts:

spyOn(SubscriptionHelper, 'unsubscribeAll');
component.ngOnDestroy();
expect(SubscriptionHelper.unsubscribeAll).toHaveBeenCalledTimes(1);

---

pros:

• I can test that the helper function was called

cons:

• I can not test that the unsubscribe function was called on a specific subscription.

---

What do you guys suggest? How do you test the cleanup in unit test?

Answer 1

I had exactly the same problem, here's my solution:

component.ts:

private subscription: Subscription;
//...
ngOnInit(): void {
    this.subscription = this.route.paramMap.subscribe((paramMap: ParamMap) => {
        // ...
    });
}

ngOnDestroy(): void {
    this.subscription.unsubscribe();
}

component.spec.ts:

let dataMock;

let storeMock: Store;
let storeStub: {
    select: Function,
    dispatch: Function
};

let paramMapMock: ParamMap;
let paramMapSubscription: Subscription;
let paramMapObservable: Observable<ParamMap>;

let activatedRouteMock: ActivatedRoute;
let activatedRouteStub: {
    paramMap: Observable<ParamMap>;
};

beforeEach(async(() => {
    dataMock = { /* some test data */ };

    storeStub = {
        select: (fn: Function) => of((id: string) => dataMock),
        dispatch: jasmine.createSpy('dispatch')
    };

    paramMapMock = {
        keys: [],
        has: jasmine.createSpy('has'),
        get: jasmine.createSpy('get'),
        getAll: jasmine.createSpy('getAll')
    };

    paramMapSubscription = new Subscription();
    paramMapObservable = new Observable<ParamMap>();

    spyOn(paramMapSubscription, 'unsubscribe').and.callThrough();
    spyOn(paramMapObservable, 'subscribe').and.callFake((fn: Function): Subscription => {
        fn(paramMapMock);
        return paramMapSubscription;
    });

    activatedRouteStub = {
        paramMap: paramMapObservable
    };

    TestBed.configureTestingModule({
       // ...
       providers: [
           { provide: Store, useValue: storeStub },
           { provide: ActivatedRoute, useValue: activatedRouteStub }
       ]
    })
    .compileComponents();
}));

// ...

it('unsubscribes when destoryed', () => {
    fixture.detectChanges();

    component.ngOnDestroy();

    expect(paramMapSubscription.unsubscribe).toHaveBeenCalled();
});

This works for me, I hope it will for you too !