To debug PHP tests in Ubuntu (assuming PHP 8.2 is the default) with Visual Studio Code:

1. Install Xdebug:

   sudo apt install php8.2-dev
   sudo pecl install xdebug

2. Enable Xdebug:

   php --ini # verify the INI file location
   sudo su
   echo 'zend_extension=/usr/lib/php/20220829/xdebug.so' >> /etc/php/8.2/cli/conf.d/99-xdebug.ini

3. Verify that it is enabled:

   $ php --version
   PHP 8.2.16 (cli) (built: Mar  7 2024 08:55:56) (NTS)
   Copyright (c) The PHP Group
   Zend Engine v4.2.16, Copyright (c) Zend Technologies
       with Zend OPcache v8.2.16, Copyright (c), by Zend Technologies
       with Xdebug v3.3.1, Copyright (c) 2002-2023, by Derick Rethans

4. Activate debugging by adding the following lines to /etc/php/8.2/cli/conf.d/99-xdebug.ini:

   xdebug.mode = debug
   xdebug.start_with_request = yes
   

5. Open VS Code and install the PHP Debug extension.

6. Activate debugging according to instructions on the extension site.

   1. In your project, go to the debugger and hit the little gear icon and choose PHP. A new launch configuration will be created for you...

7. Test debugging.

   1. Add a breakpoint in VS Code.
   2. Press the Listen for Xdebug button in Run and debug mode, the debugging session will become active.
   3. Run tests on command-line with composer test.
   4. The breakpoint will be hit in VS Code, you can examine the variables and use the debugging toolbar: