When Jest executes the test that contains the debugger statement, execution will pause and you can examine the current scope and call stack. Click the button that looks like a 'play' button in the upper right hand side of the screen to continue execution. The Chrome Developer Tools will be displayed, and a breakpoint will be set at the first line of the Jest CLI script (this is done to give you time to open the developer tools and to prevent Jest from executing before you have time to do so). Click on the address displayed in the terminal (usually something like localhost:9229) after running the above command, and you will be able to debug Jest using Chrome's DevTools. To debug in Google Chrome (or any Chromium-based browser), open your browser and go to chrome://inspect and click on 'Open Dedicated DevTools for Node', which will give you a list of available node instances you can connect to. See the reference guide for enabling reactor-tools 'debug agent', then in IntelliJ go to Preferences > Languages&Frameworks > Reactive Streams to enable support. They've been improving their async debugger, take into account when the application uses reactor-tools, etc. Note that the process will pause until the debugger has connected to it. IntelliJ has support for Reactor debugging since 2019.3 IIRC. This will run Jest in a Node process that an external debugger can connect to.

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