Unit Testing of .NET Add-In for Microsoft Office

This is how I resolved it.

1. Just about everything in my add-in runs from the Click method of a button in the UI. I have changed all those Click methods to consist only of a simple, parameterless call.

2. I then created a new file (Partial Class) called EntryPoint that had lots of very short Friend Subs, each of which was usually one or two calls to parameterised worker functions, so that all the Click methods just called into this file. So, for example, there's a function that opens a standard document and calls a "save as" into our DMS. The function takes a parameter of which document to open, and there are a couple of dozen standard documents that we use.

So I have

Private Sub btnMemo_Click(ByVal Ctrl As Microsoft.Office.Core.CommandBarButton, ByRef CancelDefault As Boolean) Handles btnMemo.Click
    DocMemo()
End Sub

in the ThisAddin and then

Friend Sub DocMemo()
    OpenDocByNumber("Prec", 8862, 1)
End Sub

in my new EntryPoints file.

3. I add a new AddInUtilities file which has

   Public Interface IAddInUtilities

#If DEBUG Then

Sub DocMemo()

#End If

End Interface


Public Class AddInUtilities
    Implements IAddInUtilities
    Private Addin as ThisAddIn

#If DEBUG Then

Public Sub DocMemo() Implements IAddInUtilities.DocMemo
    Addin.DocMemo()
End Sub

#End If

 Friend Sub New(ByRef theAddin as ThisAddIn)
     Addin=theAddin
 End Sub
 End Class

4. I go to the ThisAddIn file and add in

   Private utilities As AddInUtilities

   Protected Overrides Function RequestComAddInAutomationService() As Object If utilities Is Nothing Then utilities = New AddInUtilities(Me) End If Return utilities End Function

And now it's possible to test the DocMemo() function in EntryPoints using NUnit, something like this:

<TestFixture()> Public Class Numbering

Private appWord As Word.Application
Private objMacros As Object

<TestFixtureSetUp()> Public Sub LaunchWord()
    appWord = New Word.Application
    appWord.Visible = True

    Dim AddIn As COMAddIn = Nothing
    Dim AddInUtilities As IAddInUtilities
    For Each tempAddin As COMAddIn In appWord.COMAddIns
        If tempAddin.Description = "CobbettsMacrosVsto" Then
            AddIn = tempAddin
        End If
    Next
    AddInUtilities = AddIn.Object
    objMacros = AddInUtilities.TestObject


End Sub

<Test()> Public Sub DocMemo()


    objMacros.DocMemo()
End Sub

<TestFixtureTearDown()> Public Sub TearDown()
    appWord.Quit(False)
End Sub

End Class

The only thing you can't then unit test are the actual Click events, because you're calling into EntryPoints in a different way, ie through the RequestComAddInAutomationService interface rather than through the event handlers.

But it works!

Consider the various mocking frameworks NMock, RhinoMocks, etc. to fake the behavior of Office in your tests.