Automapper configuration in a way that is defensive, but still tight

gistfile2.txt

There are several advantages here to testing the negative case, rather than the positive
1. You're not testing what we can trust Automapper to do
2. You _are_ testing the customizations to Automapper specific to your scenario
3. Your tests will be much shorter
4. Your tests will be less brittle (if you add a field to one your source, but forget the destination, you probably also forgot to update your mapper specs too, which means nothing will be caught. This test strategy will catch that problem)

(Example above in MSpec)

TestingAutomapper.cs

        It should_map_all_fields = () =>
        {
            GetUnmappedPropertiesFor<AdvertisementEditModel, Advertisement>()
                .ShouldContainOnly(new[] { "AdLayout" });
        };

        public static string[] GetUnmappedPropertiesFor<SRC,DEST>()
        {
            return AutoMapper.Mapper.FindTypeMapFor(typeof(SRC), typeof(DEST)).GetUnmappedPropertyNames();
        }