Calling the original method from shim method

Question

While creating shims for members of types in BCLs (or of any library for that matter). We often face a situation where we want to call the original method which we have overidden (be it inside the shim delegate or outside). E.G.:

System.Fakes.ShimDateTime.NowGet = () => DateTime.Now.AddDays(-1);

In the above code, all we want to do when the DateTime.Now is called is to return a day less than the actual date. Maybe this looks like a contrived example so other (more) realistic scenarios are

1. To be able to capture and validate the argument values being passed to a particular method.
2. To be able to count the number of times a particular method/property is accessed by the code under test.

I faced with the last scenario in a real application and couldn't find an answer for Fakes on SO. However, after digging into Fakes documentation, I have found the answer so posting it along with the question for the community.

Answer 1

Fakes has a built in support for this; in fact there are two ways to achieve this.

1) Use ShimsContext.ExecuteWithoutShims() as a wrapper for the code you don't need shim behavior:

System.Fakes.ShimDateTime.NowGet = () => 
{
return ShimsContext.ExecuteWithoutShims(() => DateTime.Now.AddDays(-1));
};

2) Another approach is to set the shim to null, call the original method and restore the shim.

FakesDelegates.Func<DateTime> shim = null;
shim = () => 
{
System.Fakes.ShimDateTime.NowGet = null;
var value = ShimsContext.ExecuteWithoutShims(() => DateTime.Now.AddDays(-1));
System.Fakes.ShimDateTime.NowGet = shim;
return value;
};
System.Fakes.ShimDateTime.NowGet = shim;

Edit: Obviously the first approach is more concise and readable. SO I prefer it over explicitly declaring shim variable and removing/restoring the shim.