Jest Mocking Strategies

This project was built to support my blog post Jest Mocking Strategies.

Here are some quick links to the relevant code samples for each use case outlined in the blog post.

1. ES6 Exports

• Default export of a vanilla function
• Named export of a vanilla function
• Default export of an object
• Named export of an object
• Default export of a function that returns an object
• Named export of a function that returns an object

2. Mock behavior

• Browser functionality
  • For the whole test suite
  • In a single file
• Node modules
  • For the whole test suite
  • In a single file
• A single function of a node module
  • For the whole test suite
  • In a single file
  • In a single test

3. Common mocking errors

• The module factory of jest.mock() is not allowed to reference any out-of-scope variables
• Cannot spy the default property because it is not a function
• Cannot set property of #<Object> which has only a getter
• Warning: An update inside a test was not wrapped in act

CRA README

This project was bootstrapped with Create React App.

Available Scripts

In the project directory, you can run:

yarn start

Runs the app in the development mode.
Open http://localhost:3000 to view it in the browser.

The page will reload if you make edits.
You will also see any lint errors in the console.

yarn test

Launches the test runner in the interactive watch mode.
See the section about running tests for more information.

yarn build

Builds the app for production to the build folder.
It correctly bundles React in production mode and optimizes the build for the best performance.

The build is minified and the filenames include the hashes.
Your app is ready to be deployed!

See the section about deployment for more information.

yarn eject

Note: this is a one-way operation. Once you eject, you can’t go back!

If you aren’t satisfied with the build tool and configuration choices, you can eject at any time. This command will remove the single build dependency from your project.

Instead, it will copy all the configuration files and the transitive dependencies (webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except eject will still work, but they will point to the copied scripts so you can tweak them. At this point you’re on your own.

You don’t have to ever use eject. The curated feature set is suitable for small and middle deployments, and you shouldn’t feel obligated to use this feature. However we understand that this tool wouldn’t be useful if you couldn’t customize it when you are ready for it.

Learn More

You can learn more in the Create React App documentation.

To learn React, check out the React documentation.

Code Splitting

This section has moved here: https://facebook.github.io/create-react-app/docs/code-splitting

Analyzing the Bundle Size

This section has moved here: https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size

Making a Progressive Web App

This section has moved here: https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app

Advanced Configuration

This section has moved here: https://facebook.github.io/create-react-app/docs/advanced-configuration

Deployment

This section has moved here: https://facebook.github.io/create-react-app/docs/deployment

yarn build fails to minify

This section has moved here: https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify