Litestar Testing

---
name: litestar-testing
description: "Auto-activate for test_*.py, conftest.py, litestar.testing imports, TestClient, AsyncTestClient, create_test_client, @pytest.mark.anyio, Guard mocks, DI overrides, or Litestar handler tests. Use when testing Litestar apps, handlers, lifespan, auth, HTMX, Inertia, or database-backed integration flows. Not for generic pytest, Vitest, or non-Litestar test suites."
---

# 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](https://github.com/litestar-org/litestar-fullstack) tests
- Mocking Guards and DI dependencies
- Integration with `pytest-databases` (see `../pytest-databases/SKILL.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 tests use `@pytest.mark.anyio` (not `@pytest.mark.asyncio`); Litestar uses anyio internally
- Prefer `AsyncTestClient` for new code; `TestClient` only for legacy / sync-only flows

## Quick Reference

### TestClient vs AsyncTestClient

| Client | When to Use | Lifespan | Internals |
| --- | --- | --- | --- |
| `TestClient` | Sync test bodies, simple smoke tests | Triggered via context manager | Runs ASGI in a thread pool |
| `AsyncTestClient` | **Default for new tests** — async test bodies, lifespan-aware fixtures | Native async lifespan | Runs ASGI in the test event loop |

```python
# AsyncTestClient — preferred
from litestar.testing import AsyncTestClient

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

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

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

### anyio Setup

```python
# conftest.py
import pytest

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

```python
# 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

```python
# 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`. Mock by overriding `dependencies` or by registering a no-op guard at the app level for tests:

```python
# conftest.py
from litestar import Litestar

from app import create_app


@pytest.fixture
async def app_with_no_auth() -> Litestar:
    """App with auth Guard replaced by a no-op for tests."""
    from app.domain.accounts.guards import requires_active_user

    async def allow_all(connection, route_handler) -> None:
        return None

    app = create_app()
    # Swap the guard everywhere it's referenced (depends on app structure)
    for route in app.route_handler_method_map.values():
        ...
    return app
```

Cleaner: use DI override (preferred). If the Guard depends on a service via DI, override the service:

```python
@pytest.fixture
async def async_client(app: Litestar) -> AsyncGenerator[AsyncTestClient, None]:
    from app.domain.accounts.services import UserService

    class FakeUserService(UserService): ...

    app.dependencies["users_service"] = lambda: FakeUserService(...)
    async with AsyncTestClient(app=app) as client:
        yield client
```

### Mocking DI Dependencies

```python
from unittest.mock import AsyncMock

@pytest.fixture
async def async_client(app: Litestar) -> AsyncGenerator[AsyncTestClient, None]:
    fake_email = AsyncMock()
    app.dependencies["email_service"] = lambda: fake_email
    async with AsyncTestClient(app=app) as client:
        yield client, fake_email
```

### Integration with pytest-databases

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

```python
# 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

| Body Type | Pass via |
| --- | --- |
| JSON | `client.post("/", json={...})` |
| Form | `client.post("/", data={...})` |
| Multipart (file upload) | `client.post("/", files={"file": ("name.txt", b"content", "text/plain")})` |
| Raw bytes | `client.post("/", content=b"...")` |
| Custom content-type | `client.post("/", content=b"...", headers={"Content-Type": "..."})` |

```python
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

```python
# 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

```python
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

```python
# 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

```python
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

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

<workflow>

## 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 via `app.dependencies[name] = lambda: fake`. Avoid real network calls in tests.

### Step 5: Mock Guards When Needed

For tests that should bypass auth, override the Guard's underlying service or register a no-op Guard. Prefer DI overrides over patching internals.

### 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.

</workflow>

<guardrails>

## Guardrails

- **Use `@pytest.mark.anyio`, not `@pytest.mark.asyncio`** — Litestar runs on anyio. Mixing breaks lifespan.
- **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.
- **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 `InMemoryConfig`** — see `../litestar-email/SKILL.md`.

</guardrails>

<validation>

### 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 (with a fixture user) or are bypassed via DI override
- [ ] 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

</validation>

<example>

## Example

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

```python
# conftest.py
from collections.abc import AsyncGenerator
import pytest
from unittest.mock import AsyncMock
from litestar import Litestar
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) -> Litestar:
    from app import create_app
    from app.config import Settings

    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)


@pytest.fixture
async def async_client(app: Litestar) -> AsyncGenerator[tuple[AsyncTestClient, AsyncMock], None]:
    fake_queue = AsyncMock()
    app.dependencies["task_queues"] = lambda: type("Q", (), {"get": lambda self, name: fake_queue})()

    async with AsyncTestClient(app=app) as client:
        yield client, fake_queue
```

```python
# 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
```

</example>

---

## References Index

- **[Async Testing](references/async_testing.md)** — anyio + pytest-anyio setup, async fixtures, context manager testing, and common pitfalls.

## Cross-References

- **[litestar](../litestar/SKILL.md)** — Litestar fundamentals.
- **[pytest-databases](../pytest-databases/SKILL.md)** — Container-based DB fixtures.
- **[litestar-email](../litestar-email/SKILL.md)** — `InMemoryConfig` for email tests.
- **[litestar-saq](../litestar-saq/SKILL.md)** — 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://docs.pytest.org/en/stable/>
- <https://anyio.readthedocs.io/en/stable/testing.html>

## Shared Styleguide Baseline

- [General Principles](../litestar-styleguide/references/general.md)
- [Testing](../litestar-styleguide/references/testing.md)
- [Python](../litestar-styleguide/references/python.md)
- [Litestar](../litestar-styleguide/references/litestar.md)