What's a good way to overwrite DateTime.Now during testing?

Question

I\'ve got some (C#) code that relies on today\'s date to correctly calculate things in the future. If I use today\'s date in the testing, I have to repeat the calculation in

Answer 1

The key to successful unit testing is decoupling. You have to separate your interesting code from its external dependencies, so it can be tested in isolation. (Luckily, Test-Driven Development produces decoupled code.)

In this case, your external is the current DateTime.

My advice here is to extract the logic that deals with the DateTime to a new method or class or whatever makes sense in your case, and pass the DateTime in. Now, your unit test can pass an arbitrary DateTime in, to produce predictable results.