I had not seriously considered pg_dump / pg_restore because I assumed it would be fairly slow but I will experiment with pg_restore and template techniques this weekend and see which ones prove viable.
Another possibility a bit outside my area of expertise but what about a VM image configured to your needs that you just spin up as needed then discard when done (i.e. always spinning up the same starting image)?
I'd guess the OP is running hundreds of tests, where the data needs to be reverted/reset after each test, and each individual test might run in, say, 0.1 seconds. This is a really common technique when testing web apps. I don't think you'd want to start a VM for each of these tests, especially when the tests are small and specific.