FastApi - Override pydantic settings

README.md

Setup

pip install pytest pydantic

Run

pytest

config.py

from functools import lru_cache

from pydantic import BaseSettings


class Settings(BaseSettings):
    debug: bool = False


@lru_cache()
def get_settings():
    return Settings()

conftest.py

import pytest


@pytest.fixture
def override_settings():
    import helpers

    yield helpers.override_settings

helpers.py

import contextlib

from config import get_settings  # See https://fastapi.tiangolo.com/advanced/settings/?h=settings#settings-in-a-dependency


@contextlib.contextmanager
def override_settings(**overrides):
    settings = get_settings()
    original = {}

    try:
        for key, value in overrides.items():
            original[key] = getattr(settings, key)
            setattr(settings, key, value)

        yield
    finally:
        for key, value in original.items():
            setattr(settings, key, value)

test_override.py

import pytest


from config import get_settings
import helpers


def test_override_settings(override_settings):
    settings = get_settings()
    assert settings.debug is True

    with override_settings(debug=False):
        assert settings.debug is False

    assert settings.debug is True

    # Make sure first valid params are reverted to their original values
    with pytest.raises(AttributeError, match="'Settings' object has no attribute 'not_existant'"):
        with override_settings(debug=False, not_existant=True):
            pass

    assert settings.debug is True


@helpers.override_settings(debug=False)
def test_override_settings_decorator():
    settings = get_settings()

    assert settings.debug is False


def test_settings():
    settings = get_settings()

    assert settings.debug is True