Jest test error: ...subscribe is not a function

Question

I'm using Jest to test my Angular app (using Nx workspaces). I have a component that uses a service that I'm trying to mock. Here's the code:

myDummyService.permissions$.subscribe(permission => return // whatever);

In my test I mock the service like this:

myDummyServiceMock = {permissions$: jest.fn()}

But when the test runs and the constructor is invoked I get the following error:

`myDummyService.permissions$.subscribe is not a function`

I can't mock the subscribe function, so how can I get around this error? I tried this but I don't think it's right:

myDummyServiceMock = {permissions$: jest.fn(), subscribe: jest.fn()}

And if I do this then it works, but is it bad form?

myDummyServiceMock = {permissions$: of(true)}

Answer 1

first of all permission$ is a property, not a function, secondly, it should be an observable. Therefore it should be defined properly, for example with help of EMPTY from rxjs.

myDummyServiceMock = {permissions$: EMPTY};

Now it has subscribe, pipe and other methods.

If you want to manipulate its emits, you can use a Subject instance instead of EMPTY.