# Tweet by [@keefmoon](http://twitter.com/keefmoon) on 2018-10-24 15:46:47 > [!INFO] Archived from [original tweet](http://twitter.com/keefmoon/status/1055123445086851073) In reply to: [@nicklockwood](http://twitter.com/nicklockwood/status/1055122544393629702) @nicklockwood @rennarda @nossipova No one is suggesting that and no one does that. The date provider is a great example of where you might want to isolate system behaviour. It’s ironic that the one example he chose was almost the perfect example of why you would want to use a protocol to aid testability.