I’ve used freezetime (Python) a decent amount and have experienced some very very very funny flakes due to it.

- Sometimes your test code expects time to be moving forward

- sometimes your code might store classes into a hashmap for caching, and the cache might be built before the freeze time class override kicks in

- sometimes it happens after you have patched the classes and now your cache is weirdly poisoned

- sometimes some serialization code really cares about the exact class used

- sometimes test code acts really weird if time stops moving forward (when people use freezetime frozen=true). Selenium timeouts never clearing was funny

- sometimes your code gets a hold of the unpatched date clsss through silliness but only in one spot

Fun times.

The nicest thing is being able to just pass in a “now” parameter in things that care about time.