Document stages and jobs.

docs/gitlab/drupal/index.md

@@ -353,11 +353,15 @@ Rules, when the job should run:
 
 After the preparation and the setup of a Drupal database, we can execute tests. This happens in this stage.
 
-All tests use the two [Internal Test Stages](#internal-test-stages)
+All tests use the two [Internal Test Stages](#internal-test-stages).
 
 #### Test Code Style
 
+This job uses [PHP Code Sniffer](../../dev_tools/test.md#php-code-sniffer) and stores the artefacts in `phpcs`.
 
+Rules, when the job should run:
+
+- the code style tests are enabled by `$DISABLE_CI_TEST_CODESTYLE` != "1"
 
 #### Test PHPUnit