InvalidCastException when passing a mocked dependency into a function

Question

I am using Rhino Mocks along with nUnit to attempt to test my function IsApprovable() on an object. The function I am testing relies on another object "UserManager" that needs to be passed in. I am attempting to mock an instance of UserManager so I can specify the result of another function GetApproverDependantsList()

My issue is that when I mock the object and pass it into the function I am testing I get the following InvalidCastException:

Unable to cast object of type 'Castle.Proxies.IUserManagerProxye15b431a53ca4190b7ffbdf5e241e2bb' to type 'MyNamespace.Users.UserManager'.

I am new to this so I am not really sure if I am doing things correctly... Here is the sample mocking code I am using:

Dim helper As New BookingManagerHelper()
Dim booking As Booking = GetDummyBooking() 'method to get a booking in suitable state
Dim parameters As Collection(Of Parameter) = GetDummyParameters() 'factory method, as above
Dim mockedUserManager = MockRepository.GenerateMock(Of Users.IUserManager)()

'I have created a dummy function called GetUserCollectionWithDependant() to create the results I need the mocked function to return...
mockedUserManager.Stub(Function(x) x.GetApproverDependantsList(-1)).[Return](GetUserCollectionWithDependant(1))

'It's the line below where I find my exception...
Assert.AreEqual(True, helper.IsApprovable(booking, mockedUserManager, parameters))

The function I am attempting to test looks like the following:

Public Function IsApprovable(ByVal Booking As Booking , ByVal UserManager As Users.UserManager, Optional ByVal Parameters As Collection(Of Parameter) = Nothing) As Boolean
'various logic checks are performed on the objects passed in
End Function

Some things to note:

• UserManager implements the interface IUserManager
• UserManager contains additional properties and functions that are not defined by the interface
• UserManager also inherits from a base class (do I need to override base properties?)

I can post more code if needed. Thanks in advance.

Answer 1

I am no expert in VB.NET but IsApprovable expects a UserManager instance. The mock is of type IUserManager. Maybe you want to adjust IsApprovable to use a IUserManager instance.