Error on trying to mock out ToString() with Typemock on a Guid

Question

I am writing some unit tests and I want to mock out a user hmGuid. To do so I do the following.

string userGuidString = "b3830ce8-09aa-41ac-b759-d2af4388c706";
Guid hmGuid = Guid.NewGuid();
Isolate.WhenCalled(() => hmGuid.ToString()).WillReturn(userGuidString);

However when I do that I get the following error

No method calls found in recording block. Please check:

Are you trying to fake a field instead of a property? try to set field

Any help with this would be greatly appreciated. The ToString() is pretty standard and I've been able to mock this out on other classes before

Answer 1

Disclaimer: i work at typemock

The problem with your test is not the ToString() method, it's that you are trying to modify the behavior of a Mscorlib class, Guid, and it's not supported for the moment, but it will be possible in the near future.

More information here.