Rory Primrose

Learn from my mistakes, you don't have time to make them yourself

View project on GitHub

Testing IErrorHandler

I have previously posted (here, here and here) about using IErrorHandler to provide error handling and exception shielding in WCF services. What I haven’t discussed is how to test an implementation of this interface.

The reason for posting this is that I recently found that I had a bug in a service where un-handled exceptions weren’t being shielded from clients. This was purely because my unit tests were not validating the messages being generated for clients by the error handler.

The following method came about after a bit of research (mainly from here) and playing with code to make the solution work and easy to use. This method will assist unit testing the output of ProvideFault as it provides an easy way to extract a Fault from a Message returned by the ProvideFault method. This fault can then be tested for expected outcomes of the unit test.

private static T ReadFaultDetail<T>(Message reply) where T : class
{
    const String DetailElementName = "Detail";
    
    using (XmlDictionaryReader reader = reply.GetReaderAtBodyContents())
    {
        // Find the <soap:Detail> element
        while (reader.Read())
        {
            if (reader.NodeType == XmlNodeType.Element
                && reader.LocalName == DetailElementName)
            {
                break;
            }
        }
     
        // Check that the reader is at the detail element now that we are outside the loop
        if (reader.NodeType != XmlNodeType.Element
            || reader.LocalName != DetailElementName)
        {
            return null;
        }
    
        // Read again to move the reader into the contents of the details element
        if (!reader.Read())
        {
            return null;
        }
    
        // Deserialize the fault
        DataContractSerializer serializer = new DataContractSerializer(typeof(T));
    
        return serializer.ReadObject(reader) as T;
    }
}
Written on February 19, 2009