System.Diagnostics.Dispatchd在单体测试中如何进行MOCK

Question

实际代码如下   
     public void ShowErrorMessage(string errorMessage)
        {
            if (errorMessage == null)
            {
                errorMessage = MessageResource.ErrorCode00017;
                s_logger.Error(MessageResource.ErrorCode00017);
            }            Dispatcher.Invoke(DispatcherPriority.Normal,
                new ShowMessageHandler(UpdateErrorList), errorMessage);
        }要对这段代码进行单体测试,用NUNIT+TYPEMOCK
问题不是知道如何把Dispatcher对像进行MOCK