Snapshot Tests in React Using Jest

  • Today we’re talking about snapshot tests using Jest.
  • When writing snapshot tests using jest, you should basically just follow the next template: – – You use to create a component with desired props, transform it to JSON and then check if it matches a snapshot.
  • Here’s a more concrete example – let’s say we have a dummy component called , for which we want to write a snapshot test: – – For our Input component, it can look something like this: – – To run the test, you just need to type command in terminal….
  • Output snapshot file will be created, and when running the test next time, jest will compare that output snapshot file to our updated component.
  • Keep in mind that all of these output snapshot files should be committed alongside the modules they are covering and their tests, as they are part of the test.

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Testing in React Native — Jest & Detox –

Testing in React Native  with  Jest & Detox

#ReactJS #Jest

  • Testing can help identify bugs introduced during the development phase of the app and addressing these bugs before release means that your users will always get to use a reliable product.What kind of tests can we use?Unit tests are used to test small modular pieces of code (aka units) independently.Integration tests…
  • One of my favorite things about Jest is a feature called Snapshot testing.Snapshot tests are a very useful tool whenever you want to make sure the UI for a component or the object from an redux action or reducer does not change unexpectedly.Here’s a good explanation of what a snapshot…
  • Here’s a simple example on how to set this up.Jest tests for Pillow Pro appE2E tests: DetoxAn end-to-end test emulates a user by finding and interacting with pieces of UI in your app in a production/release environment.Detox is a gray box E2E Tests and Automation Library for Mobile Apps built by WixWe…
  • Here’s how we handle them in Detox:LoginHere’s a simple example of what a detox test for logging into the app might look like:DemoAnd finally, here’s a part of our E2E test suite in action.
  • Also, automating the tests on Bitrise CI has helped us streamline our release pipeline by preceding every release with the tests workflow.Hopefully, this post details how easy it is to test a React Native app and automate the testing process as well.

At Pillow, we release an update to our Pillow Pro app (iOS & Android) every 2 weeks or so. Most releases are over-the-air (OTA) updates that are done using CodePush, and are fully automated with…
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TDD is evil. Snapshot testing is the future. – Łukasz Sentkiewicz – Medium

TDD is evil. Snapshot testing is the future.  #javascript #tdd #testing #jest #react #reactjs

  • Simply add some tests, after you create the code.TDD in practiceLet’s take a look at an example article how to do TDD in React.Getting Started with TDD in React by @Dave CeddiaYou can find the final source in the GitHub repo.The task is to create a simple app with the following features:Allow to add new items (one string value).
  • When you have tests for the simple components that render a user’s name and email address (for example), you can later split that component up into pieces and be confident that it still works correctly.There are many uses cases where refactoring without changing functionality from the user perspective can break the tests.The original InputArea:export class InputArea extends Component { constructor(props) { super(props); this.state = { text: ” }; this.setText = this.setText.bind(this); this.handleClick = this.handleClick.bind(this); }setText(event) { this.setState({text:}); }handleClick() { }render() { return ( div input value={this.state.text} onChange={this.setText}/ button /div ); }}Can be refactored and simplified to:export class InputArea extends Component { render() { const {onSubmit} = this.props; return ( div input ref={(input} = (this.input = input)} / button onClick={() = /div ); }}The functionality won’t change, but it will break some tests.Another TDD tutorial TDD and React Components by Will VaughnThe task is to create another simple app with the following features:display list of radio inputsget onSelection callback if the input is selectedThe created component is not well designed, and it shows that using TDD doesn’t make your design perfect.There are following problems.Using a component factory (React) = (props) = {…} .
  • Tests test something, but they won’t give you 100% guarantees that the implementation is correct.Few example:It’s not verified if the input have an attribute type=”radio” .
  • jsimport * as types from function addTodo(text) { return { type: types.ADD_TODO, text }}Testing usually looks like thisimport * as actions from * as types from () = { it(‘should create an action to add a todo’, () = { const text = ‘Finish docs’ const expectedAction = { type: types.ADD_TODO, text } })})The fastest way to produce such unit tests it’s just copying code between the test file and the target source file.
  • My TDD doesn’t work in “Red”, “Greed” way, but rather in “Red”, “Red”, “Red”, “Green” way.If you just do unit testing without TDD, it’s sometimes easier to get the output from console.log(result) and then put it to to TDDI started using Facebook Jest and I test everything with snapshots.My development process looks similar to TDD, but I am able to iterate much faster.Development cycleCreate a test case with an empty snapshot.describe(‘actions’, () = { it(‘addTodo’, () = { expect(”).

I’ve been participating in Topcoder for 4 years, and during this time I completed over 250 contests. We tried to use unit tests many times, and multiple members including copilots (Project Managers…
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Jest 14.0: React Tree Snapshot Testing · Jest

  • For Facebook’s native apps we use a system called “snapshot testing”: a snapshot test system that renders UI components, takes a screenshot and subsequently compares a recorded screenshot with changes made by an engineer.
  • As a result many people stopped writing tests altogether which eventually led to instabilities.
  • With snapshot testing I do not need the output files, the snapshots are generated for free by Jest!
  • Engineers frequently told us that they spend more time writing a test than the component itself.
  • import renderer from ‘react/lib/ReactTestRenderer’ ; test ( ‘Link renders correctly’ , ( ) = > { const tree = renderer .

Read the full article, click here.

@cpojer: “Jest 14.0: React Snapshot Testing, experimental React-Native support and future plans for Jest. Try it out now!”

One of Jest’s philosophies is to provide an integrated “zero-configuration” experience. We want to make it as frictionless as possible to write good tests that are useful. We observed that when engineers are provided with ready-to-use tools, they end up writing more tests, which in turn results in stable and healthy code bases.

Jest 14.0: React Tree Snapshot Testing · Jest