Learn TypeScript 3 by Building Web Applications

Implementing positive and negative tests for getAllCountries

Now that we've seen how to test asynchronous code, let's see how we can test the getAllCountries method, which uses the Fetch API. For this one, we'll use our Fetch mock:

1. Create a new describe block as follows:

describe('getAllCountries', () => { 
    beforeEach(() => { 
        fetchMock.resetMocks(); 
    });

    // TODO add tests here 
}); 

In the beforeEach function, we use jest-fetch-mock to reset the Fetch API mock. This is useful to avoid side effects between our test cases.

2. In the following beforeEach function, add the following variable:

const dummyValidData: WorldBankApiV2CountryResponse = [{"page": 1, "pages": 7, "per_page": "50", "total": 304}, [{ "id": "ABW", "iso2Code": "AW", "name": ...