Litestar Testing

litestar-testing

Litestar-specific testing patterns built on pytest + anyio. Covers:

• TestClient vs AsyncTestClient — when to use each
• @pytest.mark.anyio setup
• App + lifespan in tests
• Fixture patterns from canonical litestar-fullstack tests
• Mocking Guards and DI dependencies
• Integration with pytest-databases (see ../pytest-databases/SKILL.md)
• Autowire discovery and cache isolation (see ../litestar-autowire/references/testing.md)
• Request body / form / multipart / header / cookie testing
• Litestar-specific assertion patterns (Response, headers, cookies)

For JS-side testing (Vitest, Testing Library, Playwright), use the upstream Vitest docs and Litestar's own JS examples. Out of scope here.

Code Style Rules

• PEP 604 unions: T | None, never Optional[T]
• Test modules MAY use from __future__ import annotations — they are pure consumer code.
• Function-based tests (not class-based)
• One assertion concern per test
• Async Litestar tests use @pytest.mark.anyio by default; do not mix AnyIO and pytest-asyncio auto modes.
• Prefer AsyncTestClient for new code; TestClient only for legacy / sync-only flows

Quick Reference

TestClient vs AsyncTestClient

# AsyncTestClient — preferred
from litestar.testing import AsyncTestClient


async def test_index(async_client: AsyncTestClient):
    resp = await async_client.get("/")
    assert resp.status_code == 200

# TestClient — legacy / sync
from litestar.testing import TestClient


def test_index(client: TestClient):
    resp = client.get("/")
    assert resp.status_code == 200

anyio Setup

# conftest.py
import pytest


@pytest.fixture
def anyio_backend() -> str:
    return "asyncio"

# tests/test_x.py
import pytest


@pytest.mark.anyio
async def test_something(): ...

Litestar's runtime is anyio-based; do not use pytest-asyncio — it conflicts.

App + Lifespan Fixture

# conftest.py
from collections.abc import AsyncGenerator
import pytest
from litestar import Litestar
from litestar.testing import AsyncTestClient

from app import create_app


@pytest.fixture
async def app() -> Litestar:
    return create_app()


@pytest.fixture
async def async_client(app: Litestar) -> AsyncGenerator[AsyncTestClient, None]:
    async with AsyncTestClient(app=app) as client:
        yield client

async with AsyncTestClient(...) runs on_startup / on_shutdown hooks and plugin lifespans (Vite, SAQ, SQLAlchemy session pool, etc.). Without the context manager, lifespan does not fire.

Mocking Guards

Guards are functions of (connection, route_handler) -> None. Test the real guard with fake identity or authorization providers. Build a fresh app with replacement providers; Litestar has no mutable app.dependency_overrides registry.

from litestar.di import Provide


@pytest.fixture
async def async_client() -> AsyncGenerator[AsyncTestClient, None]:
    fake_users_service = FakeUserService()

    async def provide_fake_users_service() -> UserService:
        return fake_users_service

    test_app = create_app(
        dependencies={
            "users_service": Provide(provide_fake_users_service),
        },
    )
    async with AsyncTestClient(app=test_app) as client:
        yield client

Mocking DI Dependencies

from collections.abc import AsyncGenerator
from unittest.mock import AsyncMock

import pytest
from litestar.di import Provide
from litestar.testing import AsyncTestClient


@pytest.fixture
async def async_client() -> AsyncGenerator[tuple[AsyncTestClient, AsyncMock], None]:
    fake_email = AsyncMock()

    async def provide_fake_email() -> AsyncMock:
        return fake_email

    app = create_app(
        dependencies={
            "email_service": Provide(provide_fake_email),
        },
    )
    async with AsyncTestClient(app=app) as client:
        yield client, fake_email

For isolated handler tests, pass replacements directly to create_async_test_client(..., dependencies={...}). Do not mutate a constructed app; rebuilding preserves dependency resolution and prevents parallel tests from sharing overrides.

Integration with pytest-databases

Combine pytest-databases fixtures with the app fixture. See ../pytest-databases/SKILL.md.

# conftest.py
pytest_plugins = ["pytest_databases.docker.postgres"]


@pytest.fixture
async def app(postgres_service) -> Litestar:
    from app import create_app
    from app.config import Settings

    settings = Settings(
        database_url=f"postgresql+asyncpg://{postgres_service.user}:{postgres_service.password}@{postgres_service.host}:{postgres_service.port}/{postgres_service.database}"
    )
    return create_app(settings=settings)

The postgres_service fixture starts a Postgres container. Inject its connection details into the app config.

Request Bodies

async def test_create_user(async_client):
    resp = await async_client.post(
        "/api/users",
        json={"name": "Alice", "email": "alice@example.com"},
    )
    assert resp.status_code == 201
    body = resp.json()
    assert body["name"] == "Alice"

Headers, Cookies, Auth

# Header
resp = await async_client.get("/", headers={"Authorization": "Bearer token"})

# Cookie
async_client.cookies.set("session", "abc123")
resp = await async_client.get("/")

# Per-request cookies
resp = await async_client.get("/", cookies={"session": "abc123"})

HTMX Requests

async def test_htmx_partial(async_client):
    resp = await async_client.get(
        "/items/list",
        headers={"HX-Request": "true", "HX-Target": "#item-list"},
    )
    assert resp.status_code == 200
    assert "<ul" in resp.text

Response Assertions

# Status
assert resp.status_code == 200

# Body
assert resp.json() == {"id": 1, "name": "Alice"}

# Headers
assert resp.headers["content-type"].startswith("application/json")
assert "HX-Trigger" in resp.headers

# Cookies (set by server)
assert "session" in resp.cookies

Parametrize

import pytest


@pytest.mark.parametrize(
    "payload, expected_status",
    [
        ({"name": "valid", "email": "a@b.co"}, 201),
        ({"name": "", "email": "a@b.co"}, 400),
        ({"name": "valid", "email": "not-email"}, 400),
    ],
)
@pytest.mark.anyio
async def test_create_user_validation(async_client, payload, expected_status):
    resp = await async_client.post("/api/users", json=payload)
    assert resp.status_code == expected_status

Coverage

pytest --cov=src --cov-report=html
pytest --cov=src --cov-fail-under=90

Workflow

Step 1: Set Up anyio Backend

Add anyio_backend fixture to conftest.py returning "asyncio". Mark async tests with @pytest.mark.anyio.

Step 2: App + Client Fixtures

Build an app fixture that returns a fresh Litestar instance per test (or per session if no shared state). Build an async_client fixture that wraps the app in AsyncTestClient via async with.

Step 3: Add Database Fixtures

If the app talks to a DB, layer in pytest-databases (postgres_service, mysql_service, etc.) and pass connection details into the app config. See ../pytest-databases/SKILL.md.

Step 4: Override DI for Externals

Mock EmailService, HTTP clients, and other side-effect-laden dependencies by constructing a fresh app or test client with replacement Provide instances. Avoid real network calls in tests.

Step 5: Mock Guards When Needed

Build a fresh app with fake identity or authorization providers. Register a no-op guard only when the test intentionally excludes authentication behavior; never patch route internals on a shared app.

Step 6: Write Tests

• One assertion concern per test.
• Use @pytest.mark.parametrize for input variations.
• Use AsyncTestClient for new code.
• Include HTMX / Inertia headers when testing those paths.

Step 7: Verify Coverage

pytest --cov=src --cov-fail-under=90. Cover handlers, services, Guards, and at least one happy-path + one error-path per route.

Guardrails

• Use @pytest.mark.anyio for new Litestar async tests — keep pytest-asyncio only when a project already uses it explicitly, and never mix auto modes.
• Always async with AsyncTestClient(app=app) — without the context manager, plugin lifespans (Vite, SAQ, SQLAlchemy) never run, and tests see a half-initialized app.
• Prefer AsyncTestClient over TestClient for new tests — the async client matches Litestar's runtime model.
• Mock side effects via DI override, not patching — keeps tests isolated from import order and global state.
• Build a fresh app for dependency replacements — Litestar has no mutable dependency-override registry, and shared app mutation races under parallel tests.
• Use pytest-databases for real DB testing — never mock SQLAlchemy / sqlspec internals; assertions on mocked queries don't catch real bugs.
• Function-based tests — no class-based test containers unless absolutely needed for shared setup.
• One assertion concern per test — failures should pinpoint a single behavior.
• Don't share state between tests — fresh app + fresh DB per test (or per module with explicit cleanup).
• Test the HTMX path with HX-Request: true — handlers that branch on request.htmx need both branches covered.
• Mock email via backend="memory" / InMemoryBackend — see ../litestar-email/SKILL.md.

Validation Checkpoint

Before delivering Litestar tests, verify:

• anyio_backend fixture returns "asyncio"
• Async tests use @pytest.mark.anyio
• AsyncTestClient is wrapped in async with (lifespan fires)
• DI dependencies (email, HTTP clients) are overridden, not patched
• DB-dependent tests use pytest-databases fixtures
• Guards either pass real auth or use a fresh app with fake identity providers
• One assertion concern per test; parametrize for input variations
• HTMX-targeted handlers have tests with HX-Request: true
• Coverage gate (--cov-fail-under) is set in CI

Example

Task: Test an account creation endpoint that hits Postgres, sends a welcome email via SAQ, and is guarded by an auth check.

# conftest.py
from collections.abc import AsyncGenerator
from unittest.mock import AsyncMock, Mock

import pytest
from litestar import Litestar
from litestar.di import Provide
from litestar.testing import AsyncTestClient

pytest_plugins = ["pytest_databases.docker.postgres"]


@pytest.fixture
def anyio_backend() -> str:
    return "asyncio"


@pytest.fixture
async def app(postgres_service) -> tuple[Litestar, AsyncMock]:
    from app import create_app
    from app.config import Settings

    fake_queue = AsyncMock()
    fake_task_queues = Mock()
    fake_task_queues.get.return_value = fake_queue

    async def provide_fake_task_queues() -> Mock:
        return fake_task_queues

    settings = Settings(
        database_url=(
            f"postgresql+asyncpg://{postgres_service.user}:{postgres_service.password}"
            f"@{postgres_service.host}:{postgres_service.port}/{postgres_service.database}"
        ),
    )
    return (
        create_app(
            settings=settings,
            dependencies={
                "task_queues": Provide(provide_fake_task_queues),
            },
        ),
        fake_queue,
    )


@pytest.fixture
async def async_client(
    app: tuple[Litestar, AsyncMock],
) -> AsyncGenerator[tuple[AsyncTestClient, AsyncMock], None]:
    test_app, fake_queue = app
    async with AsyncTestClient(app=test_app) as client:
        yield client, fake_queue

# tests/test_accounts.py
import pytest


@pytest.mark.anyio
async def test_create_account_persists_and_queues_email(async_client):
    client, fake_queue = async_client

    resp = await client.post(
        "/api/accounts",
        json={"email": "alice@example.com", "name": "Alice"},
    )

    assert resp.status_code == 201
    body = resp.json()
    assert body["email"] == "alice@example.com"
    fake_queue.enqueue.assert_awaited_once()
    args, kwargs = fake_queue.enqueue.await_args
    assert args[0] == "send_welcome_email"
    assert kwargs["email"] == "alice@example.com"


@pytest.mark.anyio
@pytest.mark.parametrize(
    "payload, expected_status",
    [
        ({"email": "valid@example.com", "name": "Valid"}, 201),
        ({"email": "", "name": "Valid"}, 400),
        ({"email": "valid@example.com", "name": ""}, 400),
    ],
)
async def test_create_account_validation(async_client, payload, expected_status):
    client, _ = async_client
    resp = await client.post("/api/accounts", json=payload)
    assert resp.status_code == expected_status

References Index

• Async Testing — anyio setup, async fixtures, context manager testing, and common pitfalls.

Cross-References

• litestar — Litestar fundamentals.
• pytest-databases — Container-based DB fixtures.
• litestar-email — backend="memory" and InMemoryBackend for email tests.
• litestar-saq — Mocking task queues.

JS-side Testing

For Vitest, Testing Library (React/Vue), and component testing, refer to upstream Vitest docs (https://vitest.dev/). This skill covers the Python/Litestar side only.

Official References

• https://docs.litestar.dev/2/usage/testing.html
• https://github.com/litestar-org/litestar/tree/v2.24.0
• https://docs.pytest.org/en/stable/
• https://anyio.readthedocs.io/en/stable/testing.html

Shared Styleguide Baseline

• General Principles
• Testing
• Python
• Litestar