This was created while fixing
MDL-40700 to skip some tests if there is anything missing for the memcache/memcached stores.
There are various unit tests requiring some extra stuff in order to be executed. That includes both installation (memcache, memcached, mongodb, ldap...) and configuration (via settings, defines...).
This issue is about to review which tests are being skipped right now in the CI servers and install and configure everything to get 0 skipped tests there.