Thanks for your reply.
Just to reproduce the issue, I simplified the test to exactly the same one you implemented above, and I still got a null hashset as a result.
I then simply copied your test class from above into my environment, and got the following exceptions:
Managed Debugging Assistant 'BindingFailure' occurred
Message=Managed Debugging Assistant 'BindingFailure' : 'The assembly with display name 'xunit.assert' failed to load in the 'LoadFrom' binding context of the AppDomain with ID 3.
The cause of the failure was: System.IO.FileNotFoundException: Could not load file or assembly 'xunit.assert' or one of its dependencies. The system cannot find the file specified.'
Message=Cannot mock 'System.Collections.Generic.Dictionary`2[System.String,System.Collections.Generic.HashSet`1[SomeClass]]'. The profiler must be enabled to mock, arrange or execute the specified target.
at Telerik.JustMock.Core.ProfilerInterceptor.ThrowElevatedMockingException(MemberInfo member)
at Telerik.JustMock.Core.MocksRepository.Create(Type type, MockCreationSettings settings)
at Telerik.JustMock.Core.ProfilerInterceptor.GuardInternal[T](Func`1 guardedAction)
at TestMethod1() in
I enabled the profiler (as indicated by the second exception), and all worked as expected. No really sure why the first exception is coming, but it works nonetheless.
Thanks for your help!