A little helper to unit test Vue components in the Cypress.io E2E test runner

A little helper to unit test Vue components in the Cypress.io E2E test runner

cypress-vue-unit-testA little helper to unit test Vue components in the open source Cypress.io E2E test runner v4.5.0+

cypress-vue-unit-test

A little helper to unit test Vue components in the open source Cypress.io E2E test runner v4.5.0+

Jump to: Comparison, Blog posts, Examples: basic, advanced, full, external, Code coverage

TLDR

  • What is this? This package allows you to use Cypress test runner to unit test your Vue components with zero effort.

Example component test

  • How is this different from vue-test-utils? Vue Test Utils uses Node, requires stubbing browser APIs, and requires users to await Vue's internal event loop. Cypress Vue Unit Test runs each component in the real browser with full power of Cypress E2E test runner: live GUI, full API, screen recording, CI support, cross-platform.

  • If you like using @testing-library/vue, you can use @testing-library/cypress for the same findBy, queryBy commands, see one of the examples in the list below

Blog posts

Install

Terminal typing vue add cypress-experimental

Vue CLI Installation

Vue CLI v3+

Recommended: One step install to existing projects with Vue CLI via experimental plugin, read Write Your First Vue Component Test

vue add cypress-experimental

If you want to install this package manually, follow manual install

Usage and Examples

// components/HelloWorld.spec.js
import { mount } from 'cypress-vue-unit-test'
import { HelloWorld } from './HelloWorld.vue'
describe('HelloWorld component', () => {
  it('works', () => {
    mount(HelloWorld)
    // now use standard Cypress commands
    cy.contains('Hello World!').should('be.visible')
  })
})

Options

You can pass additional styles, css files and external stylesheets to load, see docs/styles.md for full list.

import Todo from './Todo.vue'
const todo = {
  id: '123',
  title: 'Write more tests',
}

mount(Todo, {
  propsData: { todo },
  stylesheets: [
    'https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.css',
  ],
})

See examples below for details.

Global Vue Options

You can pass extensions (global components, mixins, modules to use) when mounting Vue component. Use { extensions: { ... }} object inside the options.

  • components - object of 'id' and components to register globally, see Components example
  • use (alias plugins) - list of plugins, see Plugins
  • mixin (alias mixins) - list of global mixins, see Mixins example
  • filters - hash of global filters, see Filters example

The intro example

Take a look at the first Vue v2 example: Declarative Rendering. The code is pretty simple

<div id="app">
  {{ message }}
</div>
var app = new Vue({
  el: '#app',
  data() {
    return { message: 'Hello Vue!' }
  },
})

It shows the message when running in the browser

Hello Vue!

Let's test it in Cypress.io (for the current version see cypress/integration/spec.js).

import { mountCallback } from 'cypress-vue-unit-test'

describe('Declarative rendering', () => {
  // Vue code from https://vuejs.org/v2/guide/#Declarative-Rendering
  const template = `
    <div id="app">
      {{ message }}
    </div>
  `

  const data = {
    message: 'Hello Vue!',
  }

  // that's all you need to do
  beforeEach(mountCallback({ template, data }))

  it('shows hello', () => {
    cy.contains('Hello Vue!')
  })

  it('changes message if data changes', () => {
    // mounted Vue instance is available under Cypress.vue
    Cypress.vue.message = 'Vue rocks!'
    cy.contains('Vue rocks!')
  })
})

Fire up Cypress test runner and have real browser (Electron, Chrome) load Vue and mount your test code and be able to interact with the instance through the reference Cypress.vue.$data and via GUI. The full power of the Cypress API is available.

Hello world tested

The list example

There is a list example next in the Vue docs.

<div id="app-4">
  <ol>
    <li v-for="todo in todos">
      {{ todo.text }}
    </li>
  </ol>
</div>
var app4 = new Vue({
  el: '#app-4',
  data: {
    todos: [
      { text: 'Learn JavaScript' },
      { text: 'Learn Vue' },
      { text: 'Build something awesome' },
    ],
  },
})

Let's test it. Simple.

import { mountCallback } from 'cypress-vue-unit-test'

describe('Declarative rendering', () => {
  // List example from https://vuejs.org/v2/guide/#Declarative-Rendering
  const template = `
    <ol>
      <li v-for="todo in todos">
        {{ todo.text }}
      </li>
    </ol>
  `

  function data() {
    return {
      todos: [
        { text: 'Learn JavaScript' },
        { text: 'Learn Vue' },
        { text: 'Build something awesome' },
      ],
    }
  }

  beforeEach(mountCallback({ template, data }))

  it('shows 3 items', () => {
    cy.get('li').should('have.length', 3)
  })

  it('can add an item', () => {
    Cypress.vue.todos.push({ text: 'Test using Cypress' })
    cy.get('li').should('have.length', 4)
  })
})

List tested

Handling User Input

The next section in the Vue docs starts with reverse message example.

<div id="app-5">
  <p>{{ message }}</p>
  <button v-on:click="reverseMessage">Reverse Message</button>
</div>
var app5 = new Vue({
  el: '#app-5',
  data: {
    message: 'Hello Vue.js!',
  },
  methods: {
    reverseMessage: function () {
      this.message = this.message.split('').reverse().join('')
    },
  },
})

We can write the test the same way

import { mountCallback } from 'cypress-vue-unit-test'

describe('Handling User Input', () => {
  // Example from https://vuejs.org/v2/guide/#Handling-User-Input
  const template = `
    <div>
      <p>{{ message }}</p>
      <button v-on:click="reverseMessage">Reverse Message</button>
    </div>
  `

  function data() {
    return { message: 'Hello Vue.js!' }
  }

  const methods = {
    reverseMessage: function () {
      this.message = this.message.split('').reverse().join('')
    },
  }

  beforeEach(mountCallback({ template, data, methods }))

  it('reverses text', () => {
    cy.contains('Hello Vue')
    cy.get('button').click()
    cy.contains('!sj.euV olleH')
  })
})

Take a look at the video of the test. When you hover over the CLICK step the test runner is showing before and after DOM snapshots. Not only that, the application is fully functioning, you can interact with the application because it is really running!

Reverse input

Component example

Let us test a complex example. Let us test a single file Vue component. Here is the Hello.vue file

<template>
  <p>{{ greeting }} World!</p>
</template>

<script>
export default {
  data() {
    return {
      greeting: 'Hello',
    }
  },
}
</script>

<style scoped>
p {
  font-size: 2em;
  text-align: center;
}
</style>

note to learn how to load Vue component files in Cypress, see Bundling section.

Do you want to interact with the component? Go ahead! Do you want to have multiple components? No problem!

import Hello from '../../components/Hello.vue'
import { mountCallback } from 'cypress-vue-unit-test'
describe('Several components', () => {
  const template = `
    <div>
      <hello></hello>
      <hello></hello>
      <hello></hello>
    </div>
  `
  const components = {
    hello: Hello,
  }
  beforeEach(mountCallback({ template, components }))

  it('greets the world 3 times', () => {
    cy.get('p').should('have.length', 3)
  })
})

Spying example

Button counter component is used in several Vue doc examples

<template>
  <button v-on:click="incrementCounter">{{ counter }}</button>
</template>

<script>
export default {
  data() {
    return {
      counter: 0,
    }
  },

  methods: {
    incrementCounter: function () {
      this.counter += 1
      this.$emit('increment')
    },
  },
}
</script>

<style scoped>
button {
  margin: 5px 10px;
  padding: 5px 10px;
  border-radius: 3px;
}
</style>

Let us test it - how do we ensure the event is emitted when the button is clicked? Simple - let us spy on the event, spying and stubbing is built into Cypress

import ButtonCounter from '../../components/ButtonCounter.vue'
import { mountCallback } from 'cypress-vue-unit-test'

describe('ButtonCounter', () => {
  beforeEach(mountCallback(ButtonCounter))

  it('starts with zero', () => {
    cy.contains('button', '0')
  })

  it('increments the counter on click', () => {
    cy.get('button').click().click().click().contains('3')
  })

  it('emits "increment" event on click', () => {
    const spy = cy.spy()
    Cypress.vue.$on('increment', spy)
    cy.get('button')
      .click()
      .click()
      .then(() => {
        expect(spy).to.be.calledTwice
      })
  })
})

The component is really updating the counter in response to the click and is emitting an event.

Spying test

XHR spying and stubbing

The mount function automatically wraps XMLHttpRequest giving you an ability to intercept XHR requests your component might do. For full documentation see Network Requests. In this repo see components/AjaxList.vue and the corresponding tests cypress/integration/ajax-list-spec.js.

// component use axios to get list of users
created() {
  axios.get(`https://jsonplaceholder.cypress.io/users?_limit=3`)
  .then(response => {
    // JSON responses are automatically parsed.
    this.users = response.data
  })
}
// test can observe, return mock data, delay and a lot more
beforeEach(mountCallback(AjaxList))
it('can inspect real data in XHR', () => {
  cy.server()
  cy.route('/users?_limit=3').as('users')
  cy.wait('@users').its('response.body').should('have.length', 3)
})
it('can display mock XHR response', () => {
  cy.server()
  const users = [{id: 1, name: 'foo'}]
  cy.route('GET', '/users?_limit=3', users).as('users')
  cy.get('li').should('have.length', 1)
    .first().contains('foo')
})

Spying on window.alert

Calls to window.alert are automatically recorded, but do not show up. Instead you can spy on them, see AlertMessage.vue and its test cypress/integration/alert-spec.js

Comparison

Feature Vue Test Utils or @testing-library/vue Cypress + cypress-vue-unit-test
Test runs in real browser
Uses full mount
Test speed 🏎 as fast as the app works in the browser
Test can use additional plugins maybe use any Cypress plugin
Test can interact with component synthetic limited API use any Cypress command
Test can be debugged via terminal and Node debugger use browser DevTools
Built-in time traveling debugger Cypress time traveling debugger
Re-run tests on file or test change
Test output on CI terminal terminal, screenshots, videos
Tests can be run in parallel ✅ via parallelization
Test against interface if using @testing-library/vue ✅ and can use @testing-library/cypress
Spying and mocking Jest mocks Sinon library
Code coverage

Examples

// components/HelloWorld.spec.js
import { mount } from 'cypress-vue-unit-test'
import { HelloWorld } from './HelloWorld.vue'
describe('HelloWorld component', () => {
  it('works', () => {
    mount(HelloWorld)
    // now use standard Cypress commands
    cy.contains('Hello World!').should('be.visible')
  })
})

Basic examples

Spec Description
Components Registers global components to use
Filters Registering global filters
Hello Testing examples from Vue2 cookbook
Mixins Registering Vue mixins
Plugins Loading additional plugins
Props Pass props to the component during mount
Slots Passing slots and scopedSlots to the component
Small examples A few small examples testing forms, buttons

Advanced examples

Spec Description
access-component Access the mounted component directly from test
i18n Testing component that uses Vue I18n plugin
mocking-axios Mocking 3rd party CommonJS modules like axios
mocking-components Mocking locally registered child components during tests
mocking-imports Stub ES6 imports from the tests
render-functions Mounting components with a render function

Full examples

We have several subfolders in examples folder.

Folder Name Description
cli An example app scaffolded using Vue CLI and the component testing added using vue add cypress-experimental command.

External examples

Repo Description
vue-component-test-example Scaffolded Vue CLI v3 project with added component tests, read Write Your First Vue Component Test.

Known problems

Bundling

How do we load this Vue file into the testing code? Using webpack preprocessor. Note that this module ships with @cypress/webpack-preprocessor 2.x that requires Webpack 4.x. If you have Webpack 3.x please add @cypress/webpack-preprocessor v1.x.

Short way

For Webpack Users

Your project probably already has webpack.config.js setup to transpile .vue files. To load these files in the Cypress tests, grab the webpack processor included in this module, and load it from the cypress/plugins/index.js file.

const {
  onFilePreprocessor,
} = require('cypress-vue-unit-test/preprocessor/webpack')
module.exports = (on) => {
  on('file:preprocessor', onFilePreprocessor('../path/to/webpack.config'))
}

Cypress should be able to import .vue files in the tests

Manual

Using @cypress/webpack-preprocessor and vue-loader. You can use cypress/plugins/index.js to load .vue files using vue-loader.

// cypress/plugins/index.js
const webpack = require('@cypress/webpack-preprocessor')
const webpackOptions = {
  module: {
    rules: [
      {
        test: /\.vue$/,
        loader: 'vue-loader',
      },
    ],
  },
}

const options = {
  // send in the options from your webpack.config.js, so it works the same
  // as your app's code
  webpackOptions,
  watchOptions: {},
}

module.exports = (on) => {
  on('file:preprocessor', webpack(options))
}

Install dev dependencies

npm i -D @cypress/webpack-preprocessor \
  vue-loader vue-template-compiler css-loader

And write a test

import Hello from '../../components/Hello.vue'
import { mountCallback } from 'cypress-vue-unit-test'

describe('Hello.vue', () => {
  beforeEach(mountCallback(Hello))

  it('shows hello', () => {
    cy.contains('Hello World!')
  })
})

Code coverage

This plugin uses babel-plugin-istanbul to automatically instrument .js and .vue files and generates the code coverage report using dependency cypress-io/code-coverage (included). The output reports are saved in the folder "coverage" at the end of the test run.

If you want to disable code coverage instrumentation and reporting, use --env coverage=false or CYPRESS_coverage=false or set in your cypress.json file

{
  "env": {
    "coverage": false
  }
}

Development

To see all local tests, install dependencies, build the code and open Cypress in GUI mode

npm install
npm run build
npm run cy:open

The build is done using tsc that transpiles all files from src to dist folder.

Debugging

Run Cypress with environment variable

DEBUG=cypress-vue-unit-test

If some deeply nested objects are abbreviated and do not print fully, set the maximum logging depth

DEBUG=cypress-vue-unit-test DEBUG_DEPTH=10

FAQ

  • If your component's static assets are not loading, you probably need to start and proxy Webpack dev server. See issue #4

Migration guide

From v2 to v3

  • update cypress/plugins/index.js file to pass the on, config arguments when creating the default preprocessor. See change, in general the new way is:
const {
  onFileDefaultPreprocessor,
} = require('cypress-vue-unit-test/preprocessor/webpack')

module.exports = (on, config) => {
  require('@cypress/code-coverage/task')(on, config)
  on('file:preprocessor', onFileDefaultPreprocessor(config))

  // IMPORTANT to return the config object
  // with the any changed environment variables
  return config
}

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Contributors

Download Details:

Author: bahmutov

GitHub: https://github.com/bahmutov/cypress-vue-unit-test

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