How override Provider in Angular 5 for only one test?

Question

In one of my unit test files, I have to mock several times the same service with different mocks.

import { MyService } from \'../services/myservice.service\'         


        

Answer 1

If you need TestBed.overrideProvider() with different values for different test cases, TestBed is frozen after call of TestBed.compileComponents() as @Benjamin Caure already pointed out. I found out that it is also frozen after call of TestBed.get().

As a solution in your 'main' describe use:

let someService: SomeService;

beforeEach(() => {
    TestBed.configureTestingModule({
        providers: [
            {provide: TOKEN, useValue: true}
        ]
    });

    // do NOT initialize someService with TestBed.get(someService) here
}

And in your specific test cases use

describe(`when TOKEN is true`, () => {

    beforeEach(() => {
        someService = TestBed.get(SomeService);
    });

    it(...)

});

describe(`when TOKEN is false`, () => {

    beforeEach(() => {
        TestBed.overrideProvider(TOKEN, {useValue: false});
        someService = TestBed.get(SomeService);
    });

    it(...)

});