Run core unit tests against object cache enabled with Redis

[spacedmonkey]

Redis is a popular technology used for object caching. Redis is used by many large WordPress hosts like pantheon, kinsta and pagely. It may even be more popular than memcache.

WordPress core unit tests, should run against redis as well as memcache, to ensure the core team can spot issues early.

[joehoyle]

My 2c, from @spacedmonkey posting for thoughts in Slack!

Is the intention here to do integration tests against popular Object-Cache drop-in implementations, so Core knows it's broken something (either via a WP bug, or bug in a given object-cache implementation); or do you want to test if Core can use Redis (i.e. data types can be mapped etc?).

As the object cache is just an interface, the irregularities between implementations of any drop-in seem to be the thing that would be uncovered by this. WP doesn’t really “run against memcache / redis”, they run against the object-cache implementation; now, running against 10 object-cache implementations (maybe across file cache, redis, memcache, apcu, mysql (yes, some people do that :P), but IMO the upstream server doesn’t really matter, the implementation is what does) could be cool, as a means of integration testing-- but I think that's really testing the popular implementations and not so much Core.