Spy method from dynamically obtained object

Question

I use mongoose and I have login function, that tries to find user and then valid his password (I will not describe here all logic of this function, but only major parts to show you my problem).

function login(req, res) {
   ...
   User.findOne(...)
       .then((user) => {
           user.validPassword(...);
           ...
       });
}

I have defined a User model that contains a validPassword method and all work fine but I have trouble to spy validPassword method.

I use Jasmine to my tests and I tried to do this in this way:

const user = new User(...);
spyOn(user, 'validPassword').and.callThrough();

expect(user.validPassword).toHaveBeenCalled(); // was never called :(

And of course I called login function. When I test findOne method in this way, it works fine, but it is simpler because I call method from User constructor:

spyOn(User, 'findOne').and.callThrough();

expect(User.findOne).toHaveBeenCalled(); // this works fine!

I think my problem is related to different instances, because findOne method resolve a new user object for me and in the tests I create a second one, what is absolutely different object, but I'm not sure about this conjecture. Can you tell me how to repair this?

Answer 1

Ok I fixed this.

1) I found solution of my problem here

2) I noticed that findOne method returns promise and then I do async task, so I had to check it with 'done' function before start testing.

function login(req, res) {
   ...
   return User.findOne(...)
       .then((user) => {
           user.validPassword(...);
           ...
       });
}

In jasmine:

beforeAll((done) => {
    spyOn(User.prototype, 'validPassword').and.callThrough();

    login(...).then(() => done());
}

it('calls validPassword', () => {
    expect(User.prototype.validPassword).toHaveBeenCalled(); // works :)
});