Core changes are tested using PHPUnit. Test 1: testing UI with mod_subsection plugin Some features of this issues are not used by core plugins yet. To test it you need to use the alpha version of mod_subsection: Decompress the mod_subsection.zip code attached to this issue into the instance "mod" folder. Check you have a "mod/subsection" folder. Login as admin and install the plugin In the terminal, init behat and run selenium. Execute all behats using the option --tags=@mod_subsection Check all tests pass. Test 2: test subsection loop prevention Do test 1 first. You will need mod_subsection installed and behat libraries loaded. Login as admin and ensure you have debug level to developer (site administration -> development -> debug messages). Go to site administration -> development -> Create testing scenarios. Once there, upload and submit the attached MDL-80190-scenario.feature file. Alternatively, you can use the terminal: php admin/tool/generator/cli/runtestscenario.php --feature="absolute/path/to/file.feature" Go to the course management and open the " MDL-80190 test" course Click on the "Subsection1" activity to display the subsection Try drag-dropping from the course index the activity "Subsection1" into the course content elements: Check dropping over the Subactivity1 does nothing Check dropping over the Section name does nothing Check dropping over the course content itself does nothing Try now to drag-droppping  from the course index the activity "Subsection2" into the course content elements: Check dropping over the Subactivity1 does nothing Check dropping over the Section name does nothing Check dropping over the content itself does nothing