Before you start, make sure you have the needed plugins installed and activated. Plugins for the most common testing libraries, such as JUnit, TestNG, and Karma are bundled in IntelliJ IDEA. Make sure that you have them activated in the Plugins dialog box in Settings:

If you skipped the installation of these plugins when you set up the IDE, click on Install Jetbrains plugin, select Unit Testing from the Category drop-down menu, and install them as shown in the following screenshot:

There are many other plugins used for unit testing coming from third-party authors. Click on Browse repositories, select Unit Testing from the Category drop-down menu, and install the desired plugin, as shown in the following screenshot. There is a big chance you will find the plugin to test a library of your choice—even the exotic one.

If you install a plugin for a specific framework, IntelliJ IDEA will provide support for it. This will include code completion, the ability to create...