Exploring the capabilities of Angular2 and Jasmine through testing

I have been working on a basic spec for a component and I'm curious about the test's behavior.

The test is designed to verify if a component is successfully created. It seems that when the test is executed, it first compiles and runs the Component class, checking certain variable states. If these conditions are not met, the test fails.

Here is an example case:

Component Constructor:

constructor(
    public route: ActivatedRoute,
    public pageService: PageService,
    private homeService: HomeService,
    public staticInfoService: StaticInfoService,
    private lang: LangService,
    public router: Router,
    public usersService: UsersService,
) {
    super(pageService, route);
    this.route.data.subscribe(data => {

        this.entityCounts = data.number;
        console.log(' +++ entity counts are ', data.number);
    });

    this.getRecentSelections();
    this.setEntityTotals();

}

The test for this component is simple - it just checks if the component exists.

Component.spec.ts

fit('should create', () => {
    expect(component).toBeTruthy();
}); 

I believe the spec is correctly set up. However, when running the test, I encounter the following error message:

TypeError: data is null in src/test.ts (line 46535)

Despite having mocked out the route with complete data, the error persists.

class MockRouter {
    navigate = jasmine.createSpy('navigate');

    data = {
        value: 100,
    };
}

expect(mockRouter.data).toBeDefined();  

Even when expecting the data to be defined, the same error arises.

If anyone can provide insight into why this issue is occurring with the test, I would greatly appreciate it. Thank you.

Answer №1

The data property type is observable. To properly handle the data, make sure to pass it as an observable type so that you can effectively subscribe to it.

Here is a recommended approach:

import 'rxjs/add/observable/of';// don't forget to import this
class MockRouter {
navigate = jasmine.createSpy('navigate');
data = Observable.of(100);   
}

Answer №2

Subscribing to observables in the constructor is generally discouraged. It's recommended to use the lifecycle method ngOnInit for subscription instead.

Another important point to note is that when writing unit tests, it is better to mock your ActivatedRoute rather than your Router. For guidance on how to mock an ActivatedRoute, refer to this question: How to properly mock an ActivatedRoute for unit testing?

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