OK, the limitation in Isolator in this case is this - because Isolator dynamically creates a class based on ITaSecurity12, it cannot be then cast to ITaSecurity6, without there being inheritance relationships between them.
Try the following: create a class that derives from both interfaces, and use that in your tests. This should be able to be case either way:
public class TaSecurityForTests : ITaSecurity6, ITaSecurity12 {...}
var fakeTaSecurity = Isolate.Fake.Instance<TaSecurityForTests>(); // pass this to your code under test
Let me know if this is any help.
Doron
Typemock Support
