Pytest Support

Pyrefly includes built-in support for pytest, the popular Python testing framework. This support focuses on fixtures and IDE workflows for navigating, annotating, and running tests.

Note: Pyrefly's pytest support is automatic when a file imports pytest. Some IDE features also depend on selecting a Python interpreter where pytest is installed.

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What is pytest?

pytest is a Python testing framework where tests are usually functions or methods named test_*. Its fixture system lets tests request reusable setup objects by naming fixture parameters.

import pytest

@pytest.fixture
def username() -> str:
    return "Ada"

def test_user(username):
    assert username == "Ada"

In this example, pytest injects the username fixture into the test function based on the parameter name.

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How Pyrefly Supports pytest

Pyrefly recognizes pytest imports and fixture decorators without requiring a plugin or manual configuration. It:

• Recognizes fixtures declared with @pytest.fixture, @pytest.fixture(...), and imported fixture aliases such as from pytest import fixture.
• Resolves fixture parameters in tests and fixtures to their fixture definitions.
• Finds references from a fixture definition to the test and fixture parameters that request it.
• Shows optional inlay hints for pytest fixture parameter types.
• Provides quick fixes that add inferred return annotations to fixtures.
• Provides quick fixes that add inferred parameter annotations to tests that use fixtures.
• Adds runnable CodeLens actions for pytest tests in supported editors.

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Fixture Navigation

Pyrefly understands pytest's fixture-by-name convention, so IDE navigation works across fixture definitions and fixture parameters in the same module.

import pytest

@pytest.fixture
def database_url() -> str:
    return "sqlite://"

def test_connection(database_url):
    assert database_url.startswith("sqlite")

Go-to-definition on the database_url parameter in test_connection jumps to the fixture definition. Find-references on the fixture name includes parameters that request that fixture.

Pyrefly also handles fixture aliases:

from pytest import fixture as reusable

@reusable
def user_id() -> int:
    return 42

def test_lookup(user_id):
    assert user_id > 0

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Fixture Type Hints and Quick Fixes

Pyrefly can infer fixture return types and offer quick fixes that make those types explicit.

import pytest

@pytest.fixture
def enabled():
    return True

def test_feature(enabled):
    assert enabled

In the editor, these quick fixes appear as code actions:

• Place the cursor inside an unannotated fixture to use Add pytest fixture type annotation, which updates the fixture to def enabled() -> bool:.
• Place the cursor on an unannotated test parameter that matches a known fixture to use Add pytest fixture parameter type annotation, which updates the test to def test_feature(enabled: bool):.
• When more than one matching annotation is available, Pyrefly can also offer batch code actions that annotate all eligible fixtures or fixture parameters in the file.

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Running pytest Tests from the Editor

In supported editors, Pyrefly shows runnable CodeLens actions above pytest tests. For example, a test method can be run using a pytest node id such as:

python -m pytest path/to/test_file.py::TestClass::test_method

This feature uses the Python interpreter selected for the workspace. If Pyrefly cannot import pytest from that interpreter, select the correct interpreter or install pytest in the active environment.

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How to Use

You do not need to enable a Pyrefly plugin or add Pyrefly-specific configuration for pytest support.

1. Install pytest in the Python environment used by your editor.
2. Install pyrefly.
3. Write pytest fixtures and tests as usual.
4. Run Pyrefly or use the Pyrefly language server in your editor.