timecop

A gem providing "time travel", "time freezing", and "time acceleration" capabilities, making it simple to test time-dependent code. It provides a unified method to mock Time.now, Date.today, and DateTime.now in a single call. Maintained by travisjeffery on GitHub, where it has earned 3,425 stars from the community.

It's actively developed around rails, ruby, test, and is a solid reference for anyone building with these tools.