Background
Mapping reference data is one of the common scenarios in BizTalk development and its usually a bit of a pain when you need to manage a lot of reference data whether it be through the BizTalk Cross Referencing features or some kind of custom solution.
I have seen many cases where only a couple of the mapping conditions are ever tested.
Approach
As usual I like to see these things tested in isolation before you start using them in your BizTalk maps so you know your mapping functions are working as expected.
This approach can be used for almost all of your reference data type mapping functions where you can take advantage of MSTests data driven tests to test lots of conditions without having to write millions of tests.
Walk Through
Rather than go into the details of this here, I'm going to call out to one of my colleagues who wrote a nice little walk through about using data driven tests a while back.
Check out Callum's blog: http://callumhibbert.blogspot.com/2009/07/data-driven-tests-with-mstest.html