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    cypress-react-unit-test
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    4.17.2 • Public • Published

    cypress-react-unit-test CircleCI Cypress.io tests renovate-app badge

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

    Jump to: Comparison, Blog posts, Presentations, Install, Examples: basic, advanced, full, external, Mocking, Style options, Code coverage, Visual testing, Common problems, Chat

    Survey

    Hi there! We are trying to collect feedback from Cypress users who need component testing. Answer a few questions in this survey about component testing to help us 🙏

    TLDR

    • What is this? This package allows you to use Cypress test runner to unit test your React components with zero effort. Here is a typical component testing, notice there is not external URL shown, since it is mounting the component directly.

    Example component test

    Comparison

    Feature Jest / Enzyme / RTL Cypress + cypress-react-unit-test
    Test runs in real browser
    Supports shallow mount
    Supports 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/react and can use @testing-library/cypress
    Spying and stubbing methods Jest mocks Sinon library
    Stubbing imports
    Stubbing clock
    Code coverage

    If you are coming from Jest + RTL world, read Test The Interface Not The Implementation.

    If you are coming from Enzyme world, check out the enzyme example.

    Blog posts

    Curious how we keep this library well-tested and all its examples up-to-date? Read the Testing Pyramids blog post.

    Presentations

    It is better to see something once than to hear about a thousand times. Watch one of the talks below to see this library in action.

    • Webinar "Component Testing with Cypress and Applitools" video, slides
    • Conference talk "Я вижу что происходит: визуальное тестирование компонентов; I see what is going on" video with Russian narration, slides in English
    • Conference talk "I See What is Going On" from JSNation video, slides
    • Conference talk "Fast and Effective ... End-to-end Tests?" from JSVidCon video, slides

    Known problems

    See issues labeled v4

    Install

    Requires Node version 8 or above.

    npm install --save-dev cypress cypress-react-unit-test

    Init

    You can use our command line wizard to give you instructions on configuring this plugin. It will try to determine which framework or bundling tool you are using and give you instructions on right configuration.

    cypress-react-unit-test init

    Or continue with manual installation:

    1. Include this plugin from your project's cypress/support/index.js
    require('cypress-react-unit-test/support')
    1. Tell Cypress how your React application is transpiled or bundled (using Webpack), so Cypress can load your components. For example, if you use react-scripts (even after ejecting) do:
    // cypress/plugins/index.js
    module.exports = (on, config) => {
      require('cypress-react-unit-test/plugins/react-scripts')(on, config)
      // IMPORTANT to return the config object
      // with the any changed environment variables
      return config
    }

    See Recipes for more examples.

    1. ⚠️ Turn the experimental component support on in your cypress.json. You can also specify where component spec files are located. For example, to have them located in src folder use:
    {
      "experimentalComponentTesting": true,
      "componentFolder": "src"
    }

    API

    • mount is the most important function, allows to mount a given React component as a mini web application and interact with it using Cypress commands
    • createMount factory function that creates new mount function with default options
    • unmount removes previously mounted component, mostly useful to test how the component cleans up after itself
    • mountHook mounts a given React Hook in a test component for full testing, see the hooks example

    Examples

    import React from 'react'
    import { mount } from 'cypress-react-unit-test'
    import { HelloWorld } from './hello-world.jsx'
    describe('HelloWorld component', () => {
      it('works', () => {
        mount(<HelloWorld />)
        // now use standard Cypress commands
        cy.contains('Hello World!').should('be.visible')
      })
    })

    Look at the examples in cypress/component folder. Here is the list of examples showing various testing scenarios.

    Basic examples

    Spec Description
    alias Retrieve mounted component by its name or alias
    alert-spec.js Component tries to use window.alert
    before-hook Mount the component from before hook to run multiple tests against it
    counter-set-state Counter component that uses this.state
    counter-use-hooks Counter component that uses useState hook
    document-spec Checks document dimensions from the component
    enzyme Several specs showing how to recreate Enzyme's setProps, setState, and setContext methods.
    emotion-spec.js Confirms the component is using @emotion/core and styles are set
    error-boundary-spec.js Checks if an error boundary component works
    fails-correctly Cypress test fails correctly when interacting with disabled elements
    pure-component-spec.js Tests stateless component
    stateless-spec.js Passes Cypress stub to the component, confirms the component calls it on click
    window In the component test, the spec window and the application's window where the component is running should be the same object
    css Shows that component with import './Button.css' works
    css modules Shows that component that using css modules styles works
    network Confirms we can use cy.route to stub / spy on component's network calls
    no-visit Component specs cannot call cy.visit
    re-render Checking how the component re-renders when its props change
    react-book-by-chris-noring Copied test examples from React Book and adapted for Cypress component tests
    react-tutorial Tests from official ReactJS tutorial copied and adapted for Cypress component tests
    stub-example Uses cy.stub as component props
    styles Add extra styles to the component during testing using style, cssFile or stylesheets mount options
    toggle-example Testing a toggle component using Cypress DOM commands
    typescript A spec written in TypeScript, shows how to use import alias
    unmount Verifies the component's behavior when it is unmounted from the DOM
    use-lodash-fp Imports and tests methods from lodash/fp dependency
    styled-components Test components that use styled-components

    plus a few smaller sanity specs in cypress/component/basic folder.

    Advanced examples

    Spec Description
    api-test Mix REST api tests that use cy-api with component tests
    app-action-example App actions against components
    context Confirms components that use React context feature work
    custom-command Wraps mount in a custom command for convenience
    forward-ref Tests a component that uses a forward ref feature
    hooks Tests several components that use React Hooks like useState, useCallback by using mountHook function
    lazy-loaded Confirms components that use React.lazy and dynamic imports work
    material-ui-example Large components demos from Material UI
    mobx-v6 Test components with MobX v6 observable
    mock-fetch Test stubs window.fetch used by component in useEffect hook
    mocking-axios Stubbing methods from a 3rd party component like axios
    mocking-component Replaced a child component with dummy component during test
    mocking-imports Stub a named ES6 import in various situations
    path-aliases Specs import components using path aliases defined in the Webpack config
    react-router-v6 Example testing a React Router v6. Both browser and in memory routers
    renderless Testing a component that does not need to render itself into the DOM
    set-timeout-example Control the clock with cy.tick and test loading components that use setTimeout
    test-retries This component is compatible with Cypress Test Retries
    testing-lib-example A spec adopted from @testing-library/react that uses @testing-library/cypress
    timers Testing components that set timers, adopted from ReactJS Testing recipes
    tutorial A few tests adopted from ReactJS Tutorial, including Tic-Tac-Toe game
    use-local-storage Use hooks to load and save items into localStorage
    portal Component test for ReactDOM.createPortal feature
    radioactive-state Testing components that use radioactive-state library
    react-bootstrap Confirms react-bootstrap components are working
    select React component Uses cypress-react-selector to find DOM elements using React component name and state values
    lazy-loaded Uses multiple chunks and async components with React.lazy + React.Suspense.
    i18n Usesreact-i18next for localizaiton.
    framer-motion Uses framer motion for javascript-based animation.
    window-env Set additional properties on the window object during test

    Full examples

    We have several subfolders in examples folder that have complete projects with just their dependencies installed in the root folder.

    Folder Name Description
    a11y Testing components' accessibility using cypress-axe
    cucumber Writing component tests using Cucumber syntax
    react-scripts-folder A project using react-scripts with component tests in cypress/component
    react-scripts A project using react-scripts with component tests in src folder, including the .env files demo.
    rollup Bundle component and specs using rollup.
    sass-and-ts Example with Webpack, Sass and TypeScript
    snapshots Component HTML and JSON snapshots using cypress-plugin-snapshots
    tailwind Testing styles built using Tailwind CSS
    using-babel Bundling specs and loaded source files using project's existing .babelrc file
    visual-sudoku Visual testing for components using open source plugin cypress-image-snapshot. For larger example with an hour long list of explanation videos, see bahmutov/sudoku.
    visual-testing-with-applitools Visual testing for components using 3rd party service Applitools.com
    visual-testing-with-happo Visual testing for components using 3rd party service Happo
    visual-testing-with-percy Visual testing for components using 3rd party service Percy.io
    webpack-file Load existing webpack.config.js file
    webpack-options Using the default Webpack options from @cypress/webpack-preprocessor to transpile JSX specs
    rewired Component tests for apps that use react-app-rewired

    External examples

    This way of component testing has been verified in a number of forked 3rd party projects.

    Repo Version Description
    try-cra-with-unit-test cypress-react-unit-test used in try-cra-with-unit-test short Hello world initialized with CRAv3
    try-cra-app-typescript cypress-react-unit-test used in try-cra-app-typescript short Hello world initialized with CRAv3 --typescript
    react-todo-with-hooks cypress-react-unit-test used in react-todo-with-hooks short Modern web application using hooks
    test-redux-examples cypress-react-unit-test used in test-redux-examples short Example apps copies from official Redux repo and tested as components
    test-react-hooks-animations cypress-react-unit-test used in test-react-hooks-animations short Testing React springs fun blob animation
    test-mdx-example cypress-react-unit-test used in test-mdx-example short Example testing MDX components using Cypress
    test-apollo cypress-react-unit-test used in test-apollo short Component testing an application that uses Apollo GraphQL library
    test-xstate-react cypress-react-unit-test used in test-xstate-react short XState component testing using Cypress
    test-react-router-v5 cypress-react-unit-test used in test-react-router-v5 short A few tests of React Router v5
    test-material-ui cypress-react-unit-test used in test-material-ui short Testing Material UI components: date pickers, lists, autocomplete
    test-d3-react-gauge cypress-react-unit-test used in test-d3-react-gauge short Testing React D3 gauges
    storybook-code-coverage cypress-react-unit-test used in storybook-code-coverage short Example app where we get 100% code coverage easily with a single integration spec and a few component specs, replacing several tools
    react-loading-skeleton cypress-react-unit-test used in react-loading-skeleton short One to one Storybook tests for React skeleton components. Uses local .babelrc settings without Webpack config
    test-swr cypress-react-unit-test used in test-swr short Component test for Zeit SWR hooks for remote data fetching
    emoji-search cypress-react-unit-test used in emoji-search short Quick component test for a fork of emoji-search
    test-custom-error-boundary cypress-react-unit-test used in test-custom-error-boundary short Play with a component that implements error boundary
    Jscrambler-Webpack-React cypress-react-unit-test used in Jscrambler-Webpack-React short Example project with its own Webpack config file
    bahmutov/integration-tests cypress-react-unit-test used in integration-tests short Example based on blog post React Integration Testing: Greater Coverage, Fewer Tests
    mobx-react-typescript-boilerplate cypress-react-unit-test used in mobx-react-typescript-boilerplate short Fork of the official Mobx example, shows clock control
    bahmutov/test-react-hook-form cypress-react-unit-test used in test-react-hook-form short Testing forms created using react-hook-form
    bahmutov/react-with-rollup cypress-react-unit-test used in react-with-rollup short Testing a React application bundled with Rollup by using @bahmutov/cy-rollup preprocessor
    bahmutov/testing-react-example cypress-react-unit-test used in testing-react-example short Described in blog post Test React Component with cypress-react-unit-test Example
    ejected-react-scripts-example cypress-react-unit-test used in ejected-react-scripts-example short Using component testing after ejecting react-scripts
    tic-tac-toe cypress-react-unit-test used in react-tic-tac-toe-example short Component and unit tests for Tic-Tac-Toe, read Tic-Tac-Toe Component Tests
    react-hooks-file-upload cypress-react-unit-test used in react-hooks-file-upload short Upload a file from the component while stubbing the server
    react-query-example cypress-react-unit-test used in react-query-example short Quick test example for components that use react-query with mock clock control
    react-testing-rails-webpacker cypress-react-unit-test used in react-testing-rails-webpacker short Project that uses @rails/webpacker to bundle files
    effective-react-tests Test a component, a Redux store, and a custom React hook

    To find more examples, see GitHub topic cypress-react-unit-test-example

    Mocking

    Using Cypress + cypress-react-unit-test your tests can mock everything:

    Options

    In most cases, the component already imports its own styles, thus it looks "right" during the test. If you need another CSS, the simplest way is to import it from the spec file:

    // src/Footer.spec.js
    import './styles/main.css'
    import Footer from './Footer'
    it('looks right', () => {
      // styles are applied
      mount(<Footer />)
    })

    Extra styles

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

    const todo = {
      id: '123',
      title: 'Write more tests',
    }
    mount(<Todo todo={todo} />, {
      stylesheets: [
        'https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.css',
      ],
    })
    Additional configuration If your React and React DOM libraries are installed in non-standard paths (think monorepo scenario), you can tell this plugin where to find them. In `cypress.json` specify paths like this:
    {
      "env": {
        "cypress-react-unit-test": {
          "react": "node_modules/react/umd/react.development.js",
          "react-dom": "node_modules/react-dom/umd/react-dom.development.js"
        }
      }
    }

    Code coverage

    If you are using plugins/cra-v3 it instruments the code on the fly using babel-plugin-istanbul and generates report using dependency cypress-io/code-coverage (included). 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
      }
    }

    Visual testing

    You can use any Cypress Visual Testing plugin to perform visual testing from the component tests. This repo has several example projects, see visual-sudoku, visual-testing-with-percy, visual-testing-with-happo, and visual-testing-with-applitools.

    For a larger Do-It-Yourself example with an hour long list of explanation videos, see bahmutov/sudoku repository. I explain how to write visual testing using open source tools in this blog post, video talk, and slides.

    Common problems

    React.lazy does not work

    Cypress only servers a single bundle and does not (yet) provide additional bundling. There are several skipped tests in this repo showing the problem. Track #524 for future work.

    Node Sass

    When using Node Sass styles, tell Cypress to use the system NodeJS rather than its bundled version. In cypress.json set option:

    {
      "nodeVersion": "system"
    }

    Find full example in sass-and-ts folder.

    Slower than Jest

    When you use cypress-X-unit-test for component testing, you might notice the tests are slower than using Jest to test the same components. Yes, that's true. A test runner could be made extremely fast if it did nothing, just check out the auchenberg/volkswagen test runner - it is blazing on CI 😉. Of course, Jest does do things, just not inside the real browser environment.

    Testing using Jest with its jsdom browser is faster than starting the real browser, loading all libraries, mounting the component and then waiting for the component to actually perform its work in response to the test's actions. But do those tests give you a true confidence that the component is working?

    Try this test 🙈

    Spoiler: it fails, proof.

    const mock = jest.fn()
    // render a component that does NOT allow any click events
    // using pointerEvents: "none" style
    const { getByRole } = render(
      <button style={{ pointerEvents: 'none' }} onClick={mock}>
        text
      </button>,
    )
    // Jest happily clicks
    fireEvent.click(getByRole('button'))
    expect(mock).not.toBeCalled()

    Cypress test on the other hand fails correctly.

    We think that using cypress-X-unit-test runs tests as fast as your application code is, and often you need to think how to slow down the Cypress Test Runner so it does not run away from the component's code, just see our blog posts dealing with test flake.

    From the developer's perspective I would ask myself: which tests do I write faster? What happens when a test fails and I need to debug the failure: which test runner allows me to debug a failed test quicker? While I am partial, I have to say, realistic Cypress tests are easier to write and debug.

    Finally, when running tests on the continuous integration service, the true test speed up comes from properly configuring dependencies caching and running tests in parallel - something we have extensively documented and consider a solved problem.

    Slow bundling

    When you bundle spec file, you are now bundling React, Read DOM and other libraries, which is might be slow. For now, you can disable inline source maps by adding to your Webpack config settings (if available) the following:

    const webpackOptions = {
      devtool: false,
    }

    Keep your eye on issue #156 for more information.

    Missing code coverage

    If you are using your custom Webpack, this plugin might be missing code coverage information because the code was not instrumented. We try to insert the babel-plugin-istanbul plugin automatically, but your bundling might not use Babel, or configure it differently, preventing plugin insertion. Please let us know by opening an issue with full reproducible details.

    See related issue #141. You can also debug the plugin's behavior by running it with DEBUG environment variable, see #debugging section.

    Gatsby.js projects not supported

    Currently, this project cannot find Webpack settings used by Gatsby.js, thus it cannot bundle specs and application code correctly. Keep an eye on #307

    Context Provider usage

    React context provider usage and API described in ./docs/providers-and-composition.md

    Chat

    We have a chat workspace at https://component-testing.slack.com/, you are welcome to join us.

    Development

    See docs/development.md

    Debugging

    You can see verbose logs from this plugin by running with environment variable

    DEBUG=cypress-react-unit-test
    

    Because finding and modifying Webpack settings while running this plugin is done by find-webpack module, you might want to enable its debug messages too.

    DEBUG=cypress-react-unit-test,find-webpack
    

    Since some objects might be deeply nested, if you see an object that is printed simply { module: { rules: [ [Object] ] } you can increase the max printed depth

    DEBUG=cypress-react-unit-test,find-webpack DEBUG_DEPTH=10
    

    Migration guide

    From v3 to v4

    The old v3 main branch is available as branch v3

    • the cy.mount is now simply import { mount } from 'cypress-react-unit-test'
    • the support file is simply require('cypress-react-unit-test/support')

    Related tools

    Same feature for unit testing components from other frameworks using Cypress

    Install

    npm i cypress-react-unit-test

    DownloadsWeekly Downloads

    15,103

    Version

    4.17.2

    License

    MIT

    Unpacked Size

    124 kB

    Total Files

    38

    Last publish

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