Understanding snapshot testing

Snapshot testing is a useful way to test that there are no unwanted changes in your user interface (UI). Jest generates snapshot files when snapshot tests are executed. The next time tests are executed, the new snapshot is compared to the previous one. If there are changes between the content of the files, the test case fails, and an error message is shown in the terminal.

To start snapshot testing, perform the following steps:

1. Install the react-test-renderer package. The --save-dev parameter means that this dependency is saved to the package.json file's devDependencies part, and it is only used for development purposes. If you type the npm install --production command in the installation phase, dependencies in the devDependencies part are not installed. So, all dependencies that are only required in the development phase should be installed using the --save-dev parameter, like this:

   npm install react-test-renderer --save-dev

2. After...