pytest-unmagic

Pytest fixtures with conventional import semantics.

Installation

pip install pytest-unmagic

Usage

Define fixtures with the unmagic.fixture decorator, and apply them to other fixtures or test functions with unmagic.use.

from unmagic import fixture, use

traces = []

@fixture
def tracer():
    assert not traces, f"unexpected traces before setup: {traces}"
    yield
    traces.clear()

@use(tracer)
def test_append():
    traces.append("hello")
    assert traces, "expected at least one trace"

A fixture must yield exactly once. The @use decorator causes the fixture to be set up and registered for tear down, but does not pass the yielded value to the decorated function. This is appropriate for fixtures that have side effects.

The location where a fixture is defined has no affect on where it can be used. Any code that can import it can use it as long as it is executed in the context of running tests and does not violate scope restrictions.

@use shorthand

If a single fixture is being applied to another fixture or test it may be applied directly as a decorator without @use(). The test in the example above could have been written as

@tracer
def test_append():
    traces.append("hello")
    assert traces, "expected at least one trace"

Applying fixtures to test classes

The @use decorator can be used on test classes, which applies the fixture(s) to every test in the class.

@use(tracer)
class TestClass:
    def test_galaxy(self):
        traces.append("Is anybody out there?")

Unmagic fixtures on unittest.TestCase tests

Unlike standard pytest fixtures, unmagic fixtures can be applied directly to unittest.TestCase tests.

Call a fixture to retrieve its value

The value of a fixture can be retrieved within a test function or other fixture by calling the fixture. This is similar to request.getfixturevalue().

@fixture
def tracer():
    assert not traces, f"unexpected traces before setup: {traces}"
    yield traces
    traces.clear()

def test_append():
    traces = tracer()
    traces.append("hello")
    assert traces, "expected at least one trace"

Fixture scope

Fixtures may declare a scope of 'function' (the default), 'class', 'module', 'package', or 'session'. A fixture will be torn down after all tests in its scope have run if any in-scope tests used the fixture.

@fixture(scope="class")
def tracer():
    traces = []
    yield traces
    assert traces, "expected at least one trace"

Autouse fixtures

Fixtures may be applied to tests automatically with @fixture(autouse=...). The value of the autouse parameter may be one of

• A test module or package path (usually __file__) to apply the fixture to all tests within the module or package.
• True: apply the fixture to all tests in the session.

A single fixture may be registered for autouse in multiple modules and packages with unmagic.autouse.

# tests/fixtures.py
from unmagic import fixture

@fixture
def a_fixture():
    ...


# tests/test_this.py
from unmagic import autouse
from .fixtures import a_fixture

autouse(a_fixture, __file__)

...


# tests/test_that.py
from unmagic import autouse
from .fixtures import a_fixture

autouse(a_fixture, __file__)

...

Magic fixture fence

It is possible to errect a fence around tests in a particular module or package to ensure that magic fixtures are not used in that namespace except with the @use(...) decorator.

from unmagic import fence

fence.install(['mypackage.tests'])

This will cause warnings to be emitted for magic fixture usages within mypackage.tests.

Accessing the pytest request object

The unmagic.get_request() function provides access to the test request object. Among other things, it can be used to retrieve fixtures defined with @pytest.fixture.

from unmagic import get_request

def test_output():
    capsys = get_request().getfixturevalue("capsys")
    print("hello")
    captured = capsys.readouterr()
    assert captured.out == "hello\n"

@use pytest fixtures

Fixtures defined with @pytest.fixture can be applied to a test or other fixture by passing the fixture name to @use. None of the built-in fixtures provided by pytest make sense to use this way, but it is a useful technique for fixtures that have side effects, such as pytest-django's db fixture.

from unmagic import use

@use("db")
def test_database():
    ...

Running the unmagic test suite

cd path/to/pytest-unmagic
pip install -e .
pytest