I've done this before, used a sqlite as a unit testing stand-in for a read-only MSSQL database my app used. Allowed me to unit test the data transform code conveniently. But that's about as far as I'd go. Running tests against one database and production against other is a great way to discover bugs in production, like the text length constraint covered in the article. And if speed is of concern but data storage is not, just launch the test database with tmpfs backed storage.