If you have a bunch of common tests that apply to many test classes you can add them via mixins. For example:
class FooTester(unittest.TestCase, MixinTests):
self.obj = Foo()
class BarTester(unittest.TestCase, MixinTests):
self.obj = Bar()
Make sure your MixinTests class doesn't subclass unittest.TestCase otherwise the test runner will try to run the tests in the mixin class itself.