I feel that trying to maintain "representative testing data" is generally not a good idea; set up the data you want/need in the test instead.

Just run PostgreSQL on your local machine, connect to that, setup a new schema for every test (fairly cheap-ish) inside a test database.

  def Test1:
    setupdb()
    obj1 = createObj1()
    obj2 = createObj2()
    have = doStuff(obj1, obj2)
    if have != want: ...

  def Test1:
    setupdb()
    obj = createObj1()
    have = doOtherStuff(obj1)
    if have != want: ...

Creating reasonably scoped reasonably contained "unit-y tests" like this means you will actually be able to understand what is going on. Too often have I seen people set up huge wads of "mock data" and then run all their tests on this. Then Test1 does something Test2 doesn't expect and you're screwed. Or worse: Test42 does something that screws Test185. Good luck with that. Or you introduce a regression somewhere and now you've got tons of data to understand.