PHPBB3-12594
* develop-olympus: [ticket/10972] Drop user deletion. [ticket/10972] Tweak user addition. [ticket/10972] Add destroy method to mock cache. [ticket/10972] Add mock null cache. [ticket/10972] Backport get_db from develop. [ticket/10972] Added explicit checks for creating duplicate users. [ticket/10972] Moved tests into appropriate places and added comments [ticket/10972] Added methods for creating and deleting basic users Conflicts: tests/mock/cache.php tests/test_framework/phpbb_functional_test_case.php
The mock cache has instrumentation methods and therefore is non-trivial to implement. For those times when we don't care that the cache caches, null cache is a simpler implementation. PHPBB3-10972
