I've created a Pyramid scaffold which integrates Alembic, a migration tool, with the standard SQLAlchemy scaffold. (It also configures the Mako template system, because I prefer Mako.)
I am also using PostgreSQL for my database. PostgreSQL supports nested transactions. This means I can setup the tables at the beginning of the test session, then start a transaction before each test happens and roll it back after the test; in turn, this means my tests operate in the same environment I expect to use in production, but they are also fast.
I based my approach on sontek's blog post, but I've refined it a bit.
I use py.test for unit tests, but to the best of my knowledge, a similar approach will work with nosetest; you just create a nosetest plugin to load in the ini file with a command line option, and have begin