Change a property in an object passed to a mocked method

Dim newTransaction As TransactionInfo
' Create the new transaction
newTransaction = New TransactionInfo( _
    barn.OperationUnitId, _
    m_Info.FocusDate, _
    Enumerations.TransactionType.DailyRegistration, _
    m_Info.CurrentUser, _
    m_Info.ResponsibleEmployeeId)
    TransactionDataProvider.Instance().Add(newTransaction)
Try
    InsertMortalities(mortalitiesToInsert, newTransaction)
Catch ex As Exception                     
    TransactionDataProvider.Instance().MarkAsDeleted(newTransaction.TransactionId.Value)
    Throw
End Try

Dim recorder As New RecordExpectations
Try
    ' mock the next future instance TransactionInfo
    Dim mockedTransaction As New TransactionInfo()
    ' value should be 1
    recorder.ExpectAndReturn(
       mockedTransaction.TransactionId.Value,1).RepeatAlways()
Finally
     recorder.Dispose()
End Try

recorder.DefaultBehavior.RepeatAlways()
recorder.ExpectAndReturn(mockedTransaction.TransactionId.Value,1)

<TestAttribute(), ExpectedException(GetType(UnitTestGeneratedException))> _
Public Sub TestSaveTransaction_NewTransactionIsMarkedAsDeletedOnError()

    ' We will throw this exception when the method tries to save the mortality
    Dim exception As New UnitTestGeneratedException

    ' Set the expectations
    Dim recorder As New RecordExpectations
    Try
        ' The method will need to instantiate a TransactionInfo object
        Dim mockedTransaction As New TransactionInfo
        ' The method will try to access the TransactionID property
        ' If we don't set this a SqlNullValueException exception will be thrown
        recorder.ExpectAndReturn(mockedTransaction.TransactionId, Constants.SqlInt32_1).RepeatAlways()

        TransactionDataProvider.Instance().Add(Nothing)

        ' When the method tries to store a mortality we throw an exception
        ' to see if it catches it to delete the transaction
        MortalityDataProvider.Instance().Store(Nothing)
        recorder.Throw(exception)

        ' The method should mark the new transaction as deleted
        TransactionDataProvider.Instance().MarkAsDeleted(1)
    Finally
        recorder.Dispose()
    End Try

    ' Create some data to make the method work
    Dim barn As New BarnInfo
    barn.OperationUnitId = Constants.SqlInt32_1

    Dim mortalitiesToInsert As New MortalityInfoCollection
    Dim mortality As New MortalityInfo
    mortalitiesToInsert.Add(mortality)

    ' This is what we want to test
    m_MortalityController.SaveTransaction(barn, Nothing, mortalitiesToInsert, Nothing, Nothing)

End Sub

By the way, I've found that trying to instantiate INullable types in the expectations recording makes TypeMock to fail.

Just because I'm curious: somewhere I saw that you can check the arguments that were passed to a mocked method. Could that be used to modify those objects?

Dim recorder As New RecordExpectations
Try
   ' Mock Add
   TransactionDataProvider.Instance().Add(Nothing)
   ' Swap the Transaction with a dummy transaction created before
   recorder.CheckArguments(New Assign(dummyTransaction))
   ' We can also VALIDATE that the correct argument was passed using
   ' recorder.CheckArguments(New Assign(dummyTransaction).AndCheck())
Finally
    recorder.Dispose()
End Try 

I have checked this and there is a problem returning Null to Nullable Types. We will fix this. Did you have a different scenario?

Imports System.Data.SqlTypes
Imports MbUnit.Framework
Imports TypeMock

<TestFixture()> _
Public Class INullableTest

    <TestAttribute()> _
    Public Sub TestReturnSqlInt32()

        Dim recorder As New RecordExpectations
        Try
            DummyClass.DoWork()
            recorder.Return(New SqlInt32(1))
        Finally
            recorder.Dispose()
        End Try

        Dim value As SqlInt32 = DummyClass.DoWork()
        Assert.IsFalse(value.IsNull)

    End Sub

End Class

Public Class DummyClass

    Public Shared Function DoWork() As SqlInt32

    End Function

End Class

[failure] INullableTest.TestReturnSqlInt32
TestCase 'INullableTest.TestReturnSqlInt32'
failed: Index was out of range. Must be non-negative and less than the size of the collection.
Nombre del parámetro: index
   System.ArgumentOutOfRangeException
   Message: Index was out of range. Must be non-negative and less than the size of the collection.
   Parameter name: index
   Source: mscorlib
   StackTrace:
   at System.Collections.ArrayList.get_Item(Int32 index)
   at ar.a()
   at TypeMock.RecorderManager.a(Object A_0, Type A_1, Boolean A_2, String A_3)
   at TypeMock.RecorderManager.a(String A_0, String A_1, Object A_2, Type A_3, Boolean A_4)
   at TypeMock.RecorderManager.a(String A_0, String A_1, Object A_2, Object[] A_3, MethodBase A_4, Object A_5)
   at TypeMock.MockManager.a(String A_0, String A_1, Object A_2, Object A_3, Object[] A_4)
   at TypeMock.InternalMockManager.getReturn(Object that, String typeName, String methodName, Object methodParameters, Object p1)
   at System.Data.SqlTypes.SqlInt32..ctor(Int32 value)
   D:DocumentosVisual Studio ProjectsTestTypeMockINullableTest.vb(14,0): at TestTypeMock.INullableTest.TestReturnSqlInt32()

It is possible to check the arguments by using CheckArguments
It is possible to modify the arguments using Assign

Dim returnValue As New SqlInt32(1)
Dim recorder As New RecordExpectations
Try
   DummyClass.DoWork()
   recorder.Return(returnValue)
Finally
   recorder.Dispose()
End Try

I think that you want to return a new SqlInt32 and not a Mock of that type. So just create the SqlInt32 outside the recording block:

DummyClass.DoWork()
recorder.Return(1) 

DummyClass.DoWork()
recorder.Return(New SqlInt32(1)) 

There is problem is with mocking new structures, as there are no instances for structures, we have to think what is supposed to happen in this scenario.

We will fixed this (and the incorrect message).