Angular 6 Unit Tests: An error was thrown in afterAll\nReferenceError: Can't find variable: $ thrown

Question

When running my unit tests, from time to time, even if they pass, at the end of all the tests running, I will get the following error.

On my Jenkins CI build running

Answer 1

My specific issue with this error was caused by not mocking sub-components of the component I was testing. In this case I had a homepage component with two sub components, which required declarations for the sub components, which I failed to mock.

As a result the sub components had real dependencies which would intermittently cause the tests to fail in this non-obvious manner (it looks like different tests are randomly failing, but it is not the case).

Mocking as follows works pretty well in this case:

@Component({
    selector: 'app-exercise',
    template: '
Mock Exercise Component
'
})
class MockExerciseComponent {
}

@Component({
    selector: 'app-user',
    template: '
Mock User Component
'
})
class MockUserComponent {
}

describe('HomepageComponent', () => {
    let component: HomepageComponent;
    let fixture: ComponentFixture;

    beforeEach(async(() => {
        TestBed.configureTestingModule({
            // note you need to mock sub components!
            declarations: [HomepageComponent, MockExerciseComponent, MockUserComponent],