# Fixtures

Each suite of tests is represented by a single YAML file, and may optionally use one or more fixtures to provide the necessary environment for tests to run.

Fixtures are implemented as nested context managers. Subclasses of `GabbiFixture` must implement `start_fixture` and `stop_fixture` methods for 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, conceptually, on the server side of the API being tested.

Fixtures may do whatever is required by the testing environment, however there are two common scenarios:

- Establishing (and then resetting when a test suite has finished) any baseline configuration settings and persistence systems required for the tests.
- Creating sample data for use by the tests.

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.

If an exception is raised while a fixture is being used, information about the exception will be stored on the fixture so that the `stop_fixture` method can decide if the exception should change how the fixture should clean up. The exception information can be found on `exc_type`, `exc_value` and `traceback` method attributes.