We just moved to the latest Test::Unit, which uses MiniTest under the hood. Because of that, I wanted to take advantage of the new MiniTest::Spec DSL to get RSpec-like syntax in Test Unit.
The problem is, when I went to the try using it, I started getting all sorts of strange duplicate key/column errors.
At first I thought it was because of a recent upgrade I had done from Postgres 9.1 to 9.2, but as I dug in deeper, I realized it was my new Spec Test. We are running our tests in transactions that we rollback on the completion of each test, MiniTest::Spec wasn’t doing this and causing all the test errors.
After hours of digging I finally found the solution to the minitest duplicate key issue here. I hope it saves you some time. Definitely did for me!
PS: The other alternative that was pointed out to me was to simply use the minitest-rails gem. I tried it but it didn’t work cleanly right out-the-box for our setup (errors in tests, etc). I was too tired to fix it up, so I’ll kick the can down the road till I need to revisit this issue, probably in upgrading to Rails 4.