ModuleFileExtensions specifies an array of file extensions your modules use. The sample application already has this file. #RESOLVE ALIASES JEST TEST WEBPACK CODE#babelrc to know which presets to run the code through. With babel -jest added, Jest will be able to work with the Babel config file. The application uses Babel for transpiling JSX and ES6 so the plugin is needed for the tests to work. #RESOLVE ALIASES JEST TEST WEBPACK INSTALL#Run the following command to install Jest and the babel -jest library which is a Jest plugin for Babel. Let's start by installing and configuring Jest. Having looked at the sample application, we'll now proceed with writing tests for it. The CountdownForm component contains a form that takes the user input and passes it to the Countdown component which starts decrementing the value every second, passing the current value to the Clock component for display. The Clock component is responsible for rendering the clock face and formatting the user's input to an MM : SS format. The functionality of the countdown timer has been separated into three components stored in the app /components folder namely Clock. You can set a time in seconds and start the countdown by clicking on the Start Countdown button. Then run the application with: $ npm start Install the necessary libraries: $ npm install To run it, first navigate to the root of the starter project: $ cd path/to/starter/CountdownTimer The sample application is a simple countdown timer created in React. In this article, we'll start with the starter project and proceed to add tests to it. In the downloaded folder, you will find three projects - one named starter with no test files, another named completed with the test files included and another named completed_with_auth0 which contains test files and also adds authentication to the application. Setting up the Sample Projectīefore looking at how tests are written, let's first look at the application we'll be testing. For this, it is recommended that you use a separate tool for browser end-to-end tests. Jest is intended for unit testing an application's logic and components rather than for testing it for any DOM quirks it might encounter. You should note though that while Jest provides browser globals such as window by using jsdom, their behavior is only an approximation of their counterparts on a real browser. Tests are run within a fake DOM implementation (via jsdom) on the command line. Jest is a Node-based runner which means that it runs tests in a Node environment as opposed to a real browser.
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