How to change the MOCK implementation of a service per unit test - jestjs

Question

How to change the implementation of a mock depending on the test.
this is the code I am trying to unit test.
open(url: string, target: string = '_self'): void {
const win = this.document.defaultView?.open(url, target);
win?.focus();
}
And below my unit test
const MockDocument = {
location: { replace: jest.fn() },
defaultView: undefined
};
const createService = createServiceFactory({
service: RedirectService,
providers: [
{ provide: DOCUMENT, useValue: MockDocument }
]
});
My strategy is to set defaultView to undefined for the first test. And inside the next test, I would change the implementation to contain the open function, like this
const defaultView = {
open: jest
.fn()
.mockImplementation((url: string, target: string = '_self') => {
url;
target;
return { focus: jest.fn().mockImplementation(() => {}) };
})
};
const MockDocument = {
location: { replace: jest.fn() },
defaultView: defaultView
};
How do I change the implementation depending on the test?
Thanks for helping
EDIT
it('should not call "open" if defaultView is not truthy', () => {
spectator.service.openFocus('foo');
expect(mockDocument.defaultView).not.toBeTruthy();
});
it('should call "open" if defaultView is truthy', () => {
//CHANGE THE IMPLEMENTATION HERE...
const spy = jest.spyOn(mockDocument.defaultView, 'open')
spectator.service.openFocus('foo');
expect(spy).toHaveBeenCalled();
});

Answer 1

You can set defaultView up as a variable and change the variable speed test.
let defaultView: any;
const MockDocument = {
location: { replace: jest.fn() },
defaultView};
beforeEach(() => {
...
});
it('should not call "open" if defaultView is not truthy', () => {
defaultView = undefined;
expect(mockDocument.defaultView).not.toBeTruthy();
});
it('should call "open" if defaultView is truthy', () => {
defaultView = {
open: jest
.fn()
.mockImplementation((url: string, target: string = '_self') => {
url;
target;
return { focus: jest.fn().mockImplementation(() => {}) };
})
};
const spy = jest.spyOn(mockDocument.defaultView, 'open')
expect(spy).toHaveBeenCalled();
});