voci¶

A concurrent test runner for async Python. voci runs your whole suite on one event loop, with every test as a concurrent asyncio task. For a suite that spends its time waiting — on a database, an ASGI app or a network stub, you can get substantial speedup, within a single process.

Tests declare what they need via dependency injection, just like FastAPI routes. There is no conftest.py or name-based lookup. A fixture is a function you import, so "go to definition" works, renames are safe, and type-checking your fixtures comes naturally.

Assertions work exactly like in pytest — assert a == b still prints a useful diff in case of failure.

Here's how some fixtures and tests could look like:

from typing import Annotated
import voci
from voci import Depends


@voci.fixture(scope="session")
async def engine() -> AsyncIterator[AsyncEngine]:
    engine = create_async_engine("sqlite+aiosqlite:///./test.db")
    yield engine
    await engine.dispose()


@voci.fixture()
async def session(engine: Annotated[AsyncEngine, Depends(engine)]) -> AsyncIterator[AsyncSession]:
    """A transaction per test, rolled back so tests stay isolated."""
    async with engine.connect() as conn:
        transaction = await conn.begin()
        yield AsyncSession(bind=conn)
        await transaction.rollback()


async def test_create_user(db: Annotated[AsyncSession, Depends(session)]) -> None:
    await db.add(User(email="alice@example.com"))
    assert await db.scalar(select(func.count()).select_from(User)) == 1

And here's what a passing run looks like:

$ voci
PASS  tests/test_users.py                        10 tests  Σ 3.84s
PASS  tests/test_orders.py                       12 tests  Σ 7.29s

22 tests · 22 passed · 1.14s wall (9.8x concurrency)

Run one after another, these tests would take 11.13 seconds. voci gets the same work done in 1.14 seconds by running them concurrently!

Install¶

You only need Python 3.13+ - voci has no dependencies.

uv add voci --dev          # or: pip install voci

Where to go next¶

• Guide — install voci, write a first test, and work through fixtures, scopes, concurrency, marks and selection one concept at a time.
• How-to — short recipes for specific tasks, once the guide is behind you.
• Migrating — take an existing pytest suite through voci-migrate: extract, audit, convert, verify.
• Reference — every public symbol, rendered from the source.