Fixtures

Constraints

We only discover package level fixtures from a conftest.py file in the root of that package.

Fixture Types

Karva supports different types of fixtures based on their scope:

Function Scope

The default scope. The fixture is created for each test function.

Module Scope

The fixture is created once per test module.

Package Scope

The fixture is created once per test package.

This means that every package that is a sub-package of the package with the fixture will create the fixture if and only if it has a module that requires the fixture.

For example, if we have the following structure:

calculator
├── src
└── tests
    ├── conftest.py
    ├── bar
    │   └── test_bar.py
    └── foo
        └── test_foo.py

If we have the following fixture in tests/conftest.py:

@fixture(scope="package")
def package_fixture():
    return "package"

And if the fixtures is used in tests/foo/test_foo.py and tests/bar/test_bar.py then fixture will be created once for the foo package and once for the bar package.

If you wanted it to only create the fixture once you should use the session scope.

Session Scope

The fixture is created once per test session.

Dependent fixtures

We support fixtures that depend on other fixtures.

from karva import fixture

@fixture
def function_fixture():
    return "function"

@fixture
def dependent_fixture(function_fixture: str) -> str:
    return function_fixture + "dependent"

def test_dependent(dependent_fixture: str):
    assert dependent_fixture == "functiondependent"

Example

uv init --lib calculator

This will give us a project that looks like this:

calculator
├── pyproject.toml
├── README.md
└── src
    └── calculator
        ├── __init__.py
        └── py.typed

We can then create our core logic in src/calculator/__init__.py.

class Calculator:
    def add(self, a: int, b: int) -> int:
        return a + b

We can then create our fixtures in tests/conftest.py.

from karva import fixture

@fixture
def calculator() -> Calculator:
    return Calculator()

We can then create our tests in tests/test_add.py.

from calculator import Calculator

def test_add(calculator: Calculator):
    assert calculator.add(1, 2) == 3

Then, we'll add karva to our project.

uv add --dev karva

We can then run our tests with uv run karva test.

uv run karva test

This will give us a report of our tests.

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