xdebug

The problem

While converting the old-style functional tests in the MongoDB project from WebTestBase to BrowserTestBase, I stumbled upon a problem: after following the drupal.org instructions to run PHPunit tests from PhpStorm, doing step-by-step debugging in the IDE worked nicely, but then stopped at the first $this->drupalLogin(); call, returning a 404 after a very long delay, although the same call running without debugging worked normally. What could be going on ?

The problem: XDebug doesn't work for Composer scripts

PhpStorm is quite convenient to debug scripts with XDebug (do you support Derick for giving us XDebug ?): just add a "Run/Debug configuration", choosing the "PHP Script" type, give a few parameters, and you can start debugging your PHP CLI scripts, using breakpoints, evaluations, etc.

Wonderful. So now, let's define such a configuration to debug a Composer script, say a Behat configuration generator from site settings for some current Drupal 8 project. Apply the configuration, run it in debug mode, and ....

...PhpStorm doesn't stop, the script runs and ends, and all breakpoints were ignored. How to actually use breakpoints in the IDE ?