DbFit is a framework written as a fit plugin of fitnesse that is dedicated to database testing.
There is no generic ANSI database implementation. See WhyNotGeneric
If the database is not implemented, a new adapter need to be added. See adding-a-new-database-adapter (ie implementation of the DbEnvironment interface where AbstractDbEnvironment has some stubs)
That is why all test fixtures have two constructors — one default, which will use the default environment, and one which allows the caller to specify the environment.