When writing unit tests for the Silverlight application, its important to write the unit test for the value converters so that you could test whether converters are working fine or not as Value Converters are most commonly used in Silverlight applications.
IValueConverter interface exposes two methods Convert & ConvertBack which are private by default and one can't call these methods explicitly in any other class. Neither you can write public wrappers on the Convert and ConvertBack methods as we can't explicitly call these methods. So we need some type of workaround to test the Value Converters.
Here is what we will have to do read full artical