PHPUNIT: 1) Install redis: https://docs.moodle.org/36/en/Redis_cache_store Make sure the php extension is installed, and you've restarted your web server. Now, run docker redis docker run --name my-redis --network host -d redis   2) Add this to config.php define( 'TEST_SESSION_REDIS_HOST' , '127.0.0.1' ); $CFG->session_handler_class = '\core\session\redis' ; $CFG->session_redis_host = '127.0.0.1' ; $CFG->session_redis_acquire_lock_timeout = 120 ; $CFG->session_redis_lock_expire = 7200 ;   3) Run unit tests: vendor/bin/phpunit lib/tests/session_redis_test.php   NOTE: The redis unit tests prior to this patch did not pass, and I am assuming were skipped in the HQ CI because the redis & drivers were not installed. Can we also fix CIME so that these are included?   Manual testing: 1) Install redis: https://docs.moodle.org/36/en/Redis_cache_store Make sure the php extension is installed, and you've restarted your web server. Now, run docker redis docker run --name my-redis --network host -d redis set up a redis cache store instance, as per the docs link above. 2) Add this to config.php   define( 'TEST_SESSION_REDIS_HOST' , '127.0.0.1' ); $CFG->session_handler_class = '\core\session\redis' ; $CFG->session_redis_host = '127.0.0.1' ; $CFG->session_redis_port = 111111 ; $CFG->session_redis_database = 0 ; // Optional, default is db 0. $CFG->session_redis_prefix = '' ; // Optional, default is don't set one. $CFG->session_redis_acquire_lock_timeout = 120 ; $CFG->session_redis_lock_expire = 7200 ; 3) Load any Moodle page in browser.   there should be an exception    Exception - Failed to connect (try 5 out of 5) to redis at 127.0.0.1:111111, error returned was: Unable to connect to host.   It can be slightly different depending on redis version. But the important part is that it exceeds number of attemts - i.e. did 5 out of 5 and failed