TIL: How to use fixtures conditionally with pytest

2022-12-27 · [Tomás Farías Santana]

Pytest has changed the way I write unit tests: As I work on them, I am constantly looking out for opportunities to use pytest.mark.parametrize to extend the scope of my tests, or pytest.fixture to manage resources used by tests. Recently, I learned it is possible to parametrize fixtures with pytest.mark.parametrize using the indirect argument:

import socket

import pytest

import app

@pytest.fixture
def db_client(request):
    match request.param:
        case "postgres":
            client = app.setup_postgres_client()
        case "TCP":
            client = app.setup_sqlite_client()
        case _:
            raise ValueError("Only UDP or TCP socket types are supported")

    yield client

    app.teardown_db_client(client)

@pytest.mark.parameterize("db_client", ["postgres", "sqlite"], indirect=True)
def test_app(my_socket):
    app.flush(db_client)
    ...

As showcased, this allows me to generate multiple test cases that each interact with a different database client¹, pretty useful if your application can work with multiple databases.

Each client should be adapted to have the same common interface so that they can be used interchangeably by our app. ↩︎

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