Any reason why you wouldn't be using the same redis instance that sidekiq uses instead? If the users want to use mockredis, they can configure sidekiq to use mockredis. 

This has the expected (to me) effect of storing sidekiq-unique-jobs' keys in another instance of mockredis. I clear my mock redis before each test, but the unique keys stay in this other instance of mockredis between my tests...

I know that it was already an issue before your PR, but you seem to have a good grasp on the problems of testing with sidekiq unique jobs and maybe the change would make sense to you.