My app uses a read-only database --- what I need to test is the
parsing code. I'd like to be able to copy the development database to
test, and run a series of unit tests based on it.
But I can't see how to stop the test system from clearing the data out
for each test.
There's a :purge task in databases.rake in vendor/rails/railties/lib/tasks. You'll wan to find a way to avoid calling that when running tests.
I'm interested to see what ideas others might share.
Leave your test database read-write, and load it up with the test/fixtures system. Then, in setup(), use Mocha to mock your .save methods (and .update, and whatever internal methods they all call), and raise a fault if anyone calls them.
Always think of mocks as a way to "change reality" - to make random dice crooked, or to change the clock time. Alternately...
Switch the DB to "read-only" in setup() and turn that off in "tear-down".
Either way, experiment by trying to .save from a scratch test, to ensure the system correctly blows up in your face. The point is to make sure at production time it does not!