Selenium/How-to/Run a subset of a test suite

Environments
This tip works if you're targeting:
 * a local MediaWiki
 * MediaWiki-Docker
 * MediaWiki-Docker-Dev
 * MediaWiki-Vagrant
 * a remote wiki
 * Beta cluster

Run Selenium tests
Usually you will run all tests.

When you're debugging, you usually want to run only one file.

If the file is big, you can run only a subset of tests, or just one test.