When running tests, you can now switch between running them against a
SQLite or PostgreSQL database. This is accomplished by modifying the
unit and acceptance tests so that when they generate and load the test
Rails application, database.yml is replaced with content that will
configure the database appropriately.
If you attempt to run tests without specifying an Appraisal, then you
will be going off of the main Gemfile. The Gemfile is not guaranteed to
contain all of the dependencies necessary to run tests, so it is very
likely that you'll get an obscure error somewhere. Instead of letting
this happen, raise a specific error.
