Recently I tried my hands on Jest - the popular JavaScript Testing Library. In my application we were using node-fetch to make API calls. I used Jest to mock and test this API calls. Here in this blog I will explain on how to mock node-fetch with Jest.
Following is my function to call the GET API.
fetch_get.js
const fetch = require('node-fetch');
module.exports = async () => {
return await fetch('http://YOUR_GET_URL').then(res => res.json());
};
Now to test this create a test file with name test.fetch_get.js
Step 1: First import the function.
const fetch_get = require('../fetch_get');
Step 2 : Mock the node-fetch with Jest
const fetch = require('node-fetch');
jest.mock('node-fetch', ()=>jest.fn())
Step 3: Create Mock response
const mockedRes = {
"success": true,
"data": [
{
id: 1,
text: 'Test Data 1'
},
{
id: 1,
text: 'Test Data 2'
}
]
};
Step 4: Add Test
describe("Test get fetch", () => {
let data;
it('It should return the data', () => {
const response = Promise.resolve({
ok: true,
status: 200,
json: () => {
return mockedRes;
},
});
fetch.mockImplementation(()=> response)
data = await fetch_get();
expect(data).toEqual(mockedRes);
});
});
In above code we have created a rest and mocked the response to return our response when we call .json() method for response. Then we are simply comparing the response. This is a very simple test. Here in stead of comparing data, you may have other tests like checking length of data or checking specific data etc.
Step 5: Run Test
Run the test with npm test or npm run test and you will see the following result.
Test get fetch
✓ It should return the data (17 ms)
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 0.313 s, estimated 1 s
Hope this helps you.
