Question

For some of my unit tests I have to call methods that require a Window as parameter. Unfortunately I can’t pass null, since the method uses the window as a reference to update the status bar where I show what is actually loaded in the real application.

So I tried to call the constructor in the unit test:

MainWindow window = new MainWindow();

But this results in the following error on the InitializeComponent method of the MainWindow constructor:

System.Windows.Markup.XamlParseException occurred
  Message='Provide value on 'System.Windows.Baml2006.TypeConverterMarkupExtension' threw an exception.' Line number '9' and line position '42'.
  Source=PresentationFramework
  LineNumber=9
  LinePosition=42
  StackTrace:
       at System.Windows.Markup.XamlReader.RewrapException(Exception e, IXamlLineInfo lineInfo, Uri baseUri)
  InnerException: System.IO.IOException
       Message=Assembly.GetEntryAssembly() returns null. Set the Application.ResourceAssembly property or use the pack://application:,,,/assemblyname;component/ syntax to specify the assembly to load the resource from.
       Source=PresentationFramework
       StackTrace:
            at MS.Internal.AppModel.ResourceContainer.GetResourceManagerWrapper(Uri uri, String& partName, Boolean& isContentFile)
            at MS.Internal.AppModel.ResourceContainer.GetPartCore(Uri uri)
            at System.IO.Packaging.Package.GetPartHelper(Uri partUri)
            at System.IO.Packaging.Package.GetPart(Uri partUri)
            at System.IO.Packaging.PackWebResponse.CachedResponse.GetResponseStream()
            at System.IO.Packaging.PackWebResponse.GetResponseStream()
            at System.IO.Packaging.PackWebResponse.get_ContentType()
            at System.Windows.Media.Imaging.BitmapDecoder.SetupDecoderFromUriOrStream(Uri uri, Stream stream, BitmapCacheOption cacheOption, Guid& clsId, Boolean& isOriginalWritable, Stream& uriStream, UnmanagedMemoryStream& unmanagedMemoryStream, SafeFileHandle& safeFilehandle)
            at System.Windows.Media.Imaging.BitmapDecoder.CreateFromUriOrStream(Uri baseUri, Uri uri, Stream stream, BitmapCreateOptions createOptions, BitmapCacheOption cacheOption, RequestCachePolicy uriCachePolicy, Boolean insertInDecoderCache)
            at System.Windows.Media.Imaging.BitmapFrame.CreateFromUriOrStream(Uri baseUri, Uri uri, Stream stream, BitmapCreateOptions createOptions, BitmapCacheOption cacheOption, RequestCachePolicy uriCachePolicy)
            at System.Windows.Media.ImageSourceConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)
            at System.Windows.Baml2006.TypeConverterMarkupExtension.ProvideValue(IServiceProvider serviceProvider)
            at MS.Internal.Xaml.Runtime.ClrObjectRuntime.CallProvideValue(MarkupExtension me, IServiceProvider serviceProvider)
       InnerException: 

So my question is, how can I instantiate or mock a window in unit testing?

Answer 1

Try the following:

if(Application.ResourceAssembly == null)
    Application.ResourceAssembly = typeof(MainWindow).Assembly;
var window = new MainWindow();