I dont know how to fix the compilation (because of the needed using)

I think I fixed it. But not sure if it's the best way.

I'm now confused, we have Throw and Throws, and both have the comments:

   /// <summary>Throw the specified exception when called.</summary>

and

<summary>Throw an exception for this call.</summary>

I'm now confused, we have Throw and Throws, and both have the comments:

   /// <summary>Throw the specified exception when called.</summary>

and

<summary>Throw an exception for this call.</summary>

Throw is part of WhenCalled, so it's meant to read as "when Xyz is called do ABC and throw DEF". When stubbing a call it reads "call ABC returns ABC / throws DEF".