VueJS - Snapshot Testing

Using Snapshot Testing

Snapshot testing is a technique for testing UI components by comparing their rendered output to a stored snapshot. This guide covers how to use snapshot testing with VueJS components.

Setting Up Snapshot Testing

To start using snapshot testing, 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'
};
                

Creating a Snapshot Test

To create a snapshot test, use Vue Test Utils to mount the component and Jest's snapshot functionality:

// MyComponent.vue




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

describe('MyComponent.vue', () => {
  it('matches the snapshot', () => {
    const wrapper = shallowMount(MyComponent);
    expect(wrapper.html()).toMatchSnapshot();
  });
});
                

Updating Snapshots

If the component's output changes intentionally, you can update the snapshot by running the Jest command with the --updateSnapshot flag:

// Update snapshots
$ npm run test -- --updateSnapshot
                

Snapshot Testing with Props and Slots

Snapshot tests can include components with props and slots to ensure all variations are covered:

// MyComponent.vue




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

describe('MyComponent.vue', () => {
  it('matches the snapshot with props and slots', () => {
    const wrapper = shallowMount(MyComponent, {
      propsData: { message: 'Hello, World!' },
      slots: { default: 'Slot content' }
    });
    expect(wrapper.html()).toMatchSnapshot();
  });
});
                

Best Practices

Follow these best practices when using snapshot testing in VueJS:

• Review Snapshots: Regularly review snapshots to ensure they accurately represent the desired output.
• Update Intentionally: Update snapshots intentionally and avoid blindly accepting changes.
• Combine with Other Tests: Combine snapshot tests with other types of tests to ensure comprehensive coverage.
• Keep Snapshots Small: Keep snapshots small and focused to make them easier to review and maintain.
• Document Changes: Document significant changes in the snapshots to keep track of the evolution of the component's output.

Summary

This guide provided an overview of snapshot testing in VueJS, including setting up Jest for snapshot testing, creating snapshot tests, updating snapshots, testing components with props and slots, and best practices. By understanding and utilizing these techniques, you can ensure that your VueJS components maintain their intended output and catch unintended changes.