# 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 required by the tests in that file.

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.

If an exception is raised when a fixture is started (in `start_fixture`) the first test in the suite using the fixture will be marked with an error using the traceback from the exception and all the tests in the suite will be skipped. This ensures that fixture failure is adequately captured and reported by test runners.

# Inner Fixtures

In some contexts (for example CI environments with a large number of tests being run in a broadly concurrent environment where output is logged to a single file) it can be important to capture and consolidate stray output that is produced during the tests and display it associated with an individual test. This can help debugging and avoids unusable output that is the result of multiple streams being interleaved.

Inner fixtures have been added to support this. These are fixtures more in line with the tradtional `unittest` concept of fixtures: a class on which `setUp` and `cleanUp` is automatically called.

`build_tests()` accepts a named parameter arguments of `inner_fixtures`. The value of that argument may be an ordered list of fixtures.Fixture classes that will be called when each individual test is set up.

An example fixture that could be useful is the FakeLogger.

Note

At this time `inner_fixtures` are not supported when using the pytest loader.