Ways to synchronize updates between Angular component.ts and its corresponding spec.ts file

Recently, I started a new position where my primary project involves working on an Angular web application. This is my first exposure to Angular, so I am in the process of learning the basics.

The main challenge I am facing currently is modifying existing component.spec.ts files to align with the changes I implement in the corresponding component.ts files.

While I believe that my alterations are functioning correctly, the unit tests fail because I suspect that the spec files need adjustments to match my updated code. Despite consulting Angular's testing documentation, I have not been able to make significant progress.

Unfortunately, I cannot share the exact code due to confidentiality reasons, and my knowledge of Angular is not advanced enough to create a mock example. However, if I abstract certain components, perhaps you can provide me with some guidance.

If, for instance, I update an existing component.ts file to include @Input() user: User; in the export class section, and introduce a method:

ngOnInit() {
     this.client = this.allClients[0].client;
     this.setClient(this.client);
   }

What modifications will be necessary in my spec file to accommodate these changes?

Currently, all 6 unit tests are failing with the error message:

TypeError: Cannot read property '0' of undefined
, which seems to indicate that I am trying to access a 'user' property that was previously unnecessary.

I understand that providing helpful feedback without seeing the entire codebase may be challenging, but any assistance or recommended resources would be greatly valued.

Answer №1

Welcome developers!

To begin, you should create a mock for the 'allClients' array and populate it with any necessary data.

For instance, your 'allClients' array could resemble this:

mockAllClients: [
    mockData: 0,
    client: 'John Smith'
]

Next, within the beforeEach() function, utilize the spyOn() function to return the mock data from its source (which might be retrieved through an HTTP call or passed into the component).

Assuming you are fetching the data from a server, the implementation could look something like this:

spyOn(someService, 'someEndpoint').and.returnValue(allClients[])

This setup will execute before each test, ensuring that the required data is available in ngOninit which is executed before every test.

Once this is set up, you can proceed to test the setClient() method independently or simulate the response by leveraging the spyOn() method described above.

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