If you are new to Pex & moles like me, you may encounter this exception while mocking any property. I have mocked one of our Dictionary and received this exception. The cause is missing one attribute on the test method.

Resolution:

If you are in Visual Studio Unit test and using Pex & Moles, then use the attribute HostType for the method.

[TestMethod]

[HostType(“Moles”)]public void UnloadAfterDequeue04()

{ 

……………………………………………

}