Mocking Api Calls | Intermediate Vuejs

Mocking API Calls in Tests

Mocking API calls in tests ensures that your components are tested in isolation and that your tests are fast and reliable. This guide covers how to mock API calls in VueJS tests using Jest.

Key Points:

Mocking API calls helps isolate components and makes tests faster and more reliable.
Jest provides utilities for mocking functions and modules, including API calls.
Mocking allows you to control the responses and behavior of API calls in your tests.

Setting Up Jest for Mocking

To start mocking API calls, ensure you have Jest set up in your VueJS project:


// Install necessary packages
$ npm install @vue/test-utils jest vue-jest babel-jest --save-dev

// Add a basic Jest configuration
// jest.config.js
module.exports = {
  moduleFileExtensions: ['js', 'json', 'vue'],
  transform: {
    '^.+\\.js$': 'babel-jest',
    '^.+\\.vue$': 'vue-jest'
  },
  testEnvironment: 'jsdom'
};

Mocking API Calls with Jest

To mock API calls, you can use Jest's mock functions. Here's an example of mocking a simple API call:


// ApiService.js
export default {
  fetchData() {
    return fetch('https://api.example.com/data')
      .then(response => response.json());
  }
};

// MyComponent.vue




// MyComponent.spec.js
import { shallowMount } from '@vue/test-utils';
import MyComponent from './MyComponent.vue';
import ApiService from './ApiService';

jest.mock('./ApiService', () => ({
  fetchData: jest.fn()
}));

describe('MyComponent.vue', () => {
  it('renders mocked data', async () => {
    ApiService.fetchData.mockResolvedValue('Mocked data');
    const wrapper = shallowMount(MyComponent);
    await wrapper.vm.$nextTick();
    expect(wrapper.text()).toContain('Mocked data');
  });
});

Mocking Axios Calls

If you are using Axios for making API calls, you can mock Axios using Jest as well:


// ApiService.js
import axios from 'axios';

export default {
  fetchData() {
    return axios.get('https://api.example.com/data')
      .then(response => response.data);
  }
};

// MyComponent.vue




// MyComponent.spec.js
import { shallowMount } from '@vue/test-utils';
import MyComponent from './MyComponent.vue';
import ApiService from './ApiService';
import axios from 'axios';

jest.mock('axios');

describe('MyComponent.vue', () => {
  it('renders mocked data', async () => {
    axios.get.mockResolvedValue({ data: 'Mocked data' });
    const wrapper = shallowMount(MyComponent);
    await wrapper.vm.$nextTick();
    expect(wrapper.text()).toContain('Mocked data');
  });
});

Handling Multiple API Calls

To handle multiple API calls in your tests, you can mock each call separately:


// ApiService.js
import axios from 'axios';

export default {
  fetchData() {
    return axios.get('https://api.example.com/data')
      .then(response => response.data);
  },
  fetchOtherData() {
    return axios.get('https://api.example.com/other-data')
      .then(response => response.data);
  }
};

// MyComponent.vue




// MyComponent.spec.js
import { shallowMount } from '@vue/test-utils';
import MyComponent from './MyComponent.vue';
import ApiService from './ApiService';
import axios from 'axios';

jest.mock('axios');

describe('MyComponent.vue', () => {
  it('renders mocked data and other data', async () => {
    axios.get.mockImplementation(url => {
      if (url === 'https://api.example.com/data') {
        return Promise.resolve({ data: 'Mocked data' });
      } else if (url === 'https://api.example.com/other-data') {
        return Promise.resolve({ data: 'Mocked other data' });
      }
    });
    const wrapper = shallowMount(MyComponent);
    await wrapper.vm.$nextTick();
    expect(wrapper.text()).toContain('Mocked data');
    expect(wrapper.text()).toContain('Mocked other data');
  });
});

Best Practices

Follow these best practices when mocking API calls in tests:

Mock API Calls: Always mock API calls to isolate your component tests from external dependencies and ensure they run quickly and reliably.
Use Jest's Mock Functions: Use Jest's mock functions to control the behavior of your API calls and return different responses as needed.
Test Edge Cases: Test edge cases and error handling by mocking different API responses, including errors and empty data.
Keep Tests Independent: Ensure your tests do not depend on each other by resetting mock implementations between tests.
Document Mock Implementations: Document your mock implementations to make it clear what behavior is being tested and why.

Summary

This guide provided an overview of mocking API calls in VueJS tests, including setting up Jest for mocking, mocking simple API calls, mocking Axios calls, handling multiple API calls, and best practices. By understanding and utilizing these techniques, you can ensure that your component tests are fast, reliable, and isolated from external dependencies.

VueJS - Mocking API Calls