Sometimes it is necessary to override the system clock during controlled, simulated experiments. It's really quite simple. Clockworks offers the following features.

The SystemClock overrides the default DateTime, providing an easy to use alternative to DateTime.Now and DateTime.UtcNow.

SystemClock is IDisposable, so it allows you to wrap a using statement around an instance when you require control over the clock.

public interface ISystemClock : IDisposable
{
   // ...
}

SystemClock installations may be stacked. That is, you can stack instances of clock overrides using the Install feature. This returns the same disposable instance as creating a new instance yourself. When it disposes, the disposing instance is popped off the stack, thus exposing either the previously installed instance, or the bare system DateTime.

using (var installed = SystemClock.Install(new DateTime(1999, 1, 1)))
{
   // ...
}

The SystemClock.Now and SystemClock.UtcNow properties expose the bare system clock, or the overridden system clock after calling Install.

using (var installed = SystemClock.Install(...))
{
    Console.WriteLine("This is the new Now: {0}", SystemClock.Now);
    Console.WriteLine("This is the new UtcNow: {0}", SystemClock.UtcNow);
}

You may use an ISystemClock instance to feed your DateTime concerns, but using the ISystemClock.Now and ISystemClock.UtcNow, respectively, after creating a new instance.

using (ISystemClock instance = new SystemClock(...))
{
    Console.WriteLine("This is the new Now: {0}", instance.Now);
    Console.WriteLine("This is the new UtcNow: {0}", instance.UtcNow);
}

Because the instance properties are implemented via the interface, you do need to "see" the instance as an interface. This is due to the fact that there are static properties by the same name for the SystemClock class, which precludes the same instance properties from being named.

While it feels like a limitation, this can prove advantageous, especially in more robust applications where you require some level of Dependency Injection, Inversion of Control, or other such factories and life cycle managers.

That's it. Pretty straightforward.

I am considering adding in some stopwatch and timer features if time permits and necessity dictates.

Enjoy!