I wouldn't recommend the keyword approach. For a small app (one or two tables) this might work ok, but for larger apps this will get quite unweildly .
I recommend either a) creating a new database for testing and adjusting the dev copy's data connection to point to it (this is best option - the dbname also won't get clobbered in a design refresh). b) is to leave the connection the same as production so you have two versions of the app (dev and prod) pointing to the same data source. The danger with this approach is that you may"accidentally" destroy the production data during your testing so use this approach with caution!
The simplest approach is usually the best :-)