In gabbi, fixtures are implemented as nested context managers. Subclasses of GabbiFixture must implement start_fixture and stop_fixture methods creating and destroying, respectively, any resources managed by the fixture. While the subclass may choose to implement __init__ it is important that no exceptions are thrown in that method, otherwise the stack of context managers will fail in unexpected ways. Instead initialization of real resources should happen in start_fixture.
At this time there is no mechanism for the individual tests to have any direct awareness of the fixtures. The fixtures exist, instead, on the inside of the API being tested. Their most common function is expected to be the creation of sample data, by whatever means make sense for the system being tested.
If a fixture raises unittest.case.SkipTest during start_fixture all the tests in the current file will be skipped. This makes it possible to skip the tests if some optional configuration (such as a particular type of database) is not available.