From the perspective of a module author, this allows you to write tests against a datbase without knowing precisely which databases will be used. you call test::database->handles() and you get a number of dbi handles against which you can run your tests. you can specify which databases you are willing to support.

from the perspective of someone installing a perl module which uses test::database, you put a config file in your home directory which explains how to connect to non-file based databases. file based databases do not normally needed configuration so long as the dbd driver is available.