Like many companies that require all access be through stored procedures, we seem to have a lot of business logic locked away in sprocs. These things are just plain hard to tes
We had a very thin Data Access layer which basically facaded stored procedures to look like C# methods. Our NUnit test-suite then had SetUp/TearDown to create/rollback a transaction and test methods that called into DAL. Nothing fancy, and proved to be easier to maintain than TSQLUnit test-suite.