Nrthugu

I can't get my head around how to unit test this class' Invoke-Method:

Option Strict On

Imports System.Windows.Interactivity



Public Class ViewErrorCounterAction

    Inherits TriggerAction(Of DependencyObject)



    Public Shared ReadOnly ViewErrorCounterProperty As DependencyProperty = DependencyProperty.Register("ViewErrorCounter",GetType(Integer),GetType(ViewErrorCounterAction))



    Sub New()

        ViewErrorCounter = 0 

    End Sub



    Public Property ViewErrorCounter As Integer

        Get

            Return CType(GetValue(ViewErrorCounterProperty), Integer)

        End Get

        Set

            SetValue(ViewErrorCounterProperty, Value)

        End Set

    End Property



    Protected Overrides Sub Invoke(parameter As Object)

        Dim e = CType(parameter, ValidationErrorEventArgs)

        If (e.Action = ValidationErrorEventAction.Added) Then

            ViewErrorCounter = ViewErrorCounter + 1

        ElseIf (e.Action = ValidationErrorEventAction.Removed) Then

            ViewErrorCounter = ViewErrorCounter - 1

        End If

    End Sub



End Class

I managed to call the invoke method and also pass the right parameter by using this code but struggle with the creation of the ValidationErrorEventArgs object as it's constructor is internal:

Sub Invoke_ValidationerrorEventEinAufruf_ErrorCounterIst1()

    Dim _viewErrorCounterAction = New ViewErrorCounterAction

    dim _manualTrigger = New ManualTrigger

    _manualTrigger.Actions.Add(_viewErrorCounterAction)



    'This line won't work because the constructor is internal

    Dim ev = New ValidationErrorEventArgs(New ValidationError(Nothing, Nothing), ValidationErrorEventAction.Added)



    _manualTrigger.Invoke(ev)

    Dim result = _viewErrorCounterAction.ViewErrorCounter

    Assert.That(result, [Is].EqualTo(1))

End Sub



'with help of https://stackoverflow.com/a/12977944/2582968

Public Class ManualTrigger

    Inherits Interactivity.TriggerBase(Of DependencyObject)



    Public Sub Invoke(parameter As Object)

        Me.InvokeActions(parameter)

    End Sub

End Class

I experimented with Activator.CreateInstance to create ValidationErrorEventArgs but wasn't successful yet. Since this whole activator story seems to me as being far out from an ordinary unit test's complexity, I'd appreciate any hints on how to best test this code. If the Activator is my only option, I'd be happy about some help on how to create that ValidationErrorEventArgs-Object.

You could create a ValidationErrorEventArgs using reflection:

Dim validationErrorEventArgsConstructorInfo As ConstructorInfo = GetType(ValidationErrorEventArgs) _

    .GetConstructors(BindingFlags.NonPublic Or BindingFlags.Instance) _

    .First()



Dim validationErrorEventArgsInstance As ValidationErrorEventArgs = validationErrorEventArgsConstructorInfo _

    .Invoke(New Object() {New ValidationError(New DataErrorValidationRule(), New Object()), ValidationErrorEventAction.Added})