Angular 17+ testing services with signals and effects

I have a service A which exposes a public method that sets/updates a private signal in the service. Anytime the value of the signal in service A changes, it triggers an effect (called in the constructor of the service), that calls a private method of service A.

The private method is used to call a number of other different services' methods, but for the sake of simplicity let's just say that it's only one service - service B, and a exposed method of service B.

The code works as it's supposed to, but I need to write tests for this system and it seems like I cannot wrap my head around how services with signals, especially the triggered effects.

The goal of the test is to verify that once public method of service A (which updates the signal) is called, that also the whole chain happens, i.e. eventually public method of service B is called.

How can I get the test to work with Signals?

Example:

@Injectable({
providedIn: 'root'
})
export class ServiceA {
private signalA: Signal<number> = signal(0);

constructor(private readonly serviceB: ServiceB) {
effect(() => {
const signalAValue = signalA();
this.privateMethod(signalAValue);
});
}

public publicMethodA(value: number): void {
this.signalA.update(value);
}

private privateMethodA(arg: number): void {
this.serviceB.publicMethodB(arg)
}
}


Test for ServiceA:

describe('ServiceA', () => {
let serviceA: ServiceA;
let serviceB: ServiceB;

beforeEach(() => {
TestBed.configureTestingModule({
providers: [
ServiceA,
ServiceB
]
});

serviceA = TestBed.inject(ServiceA);
serviceB = TestBed.inject(ServiceB);
});

it('should call publicMethodB of ServiceB when publicMethodA of ServiceA is called', fakeAsync(() => {
jest.spyOn(serviceA, 'publicMethodA');
service.publicMethod(1);

expect(serviceB.publicMethodB).toHaveBeenCalled();
}));
});


Test fails with:

Expected number of calls: >= 1
Received number of calls: 0

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