When writing Rails migrations, it is good to define, when possible, what should happen when migrating up and what should happen when migrating down. You'll then want to check that both the up and down work. This can be accomplished using the following one-liner:
$ rake db:migrate && rake db:migrate:redo
The rake db:migration
does what we would expect applying our new migration
and showing us that our up works. The rake db:migrate:redo
first
performs a rollback, showing us that our down works, and then migrates
back up again. We now know that our latest migration works going both
directions.