Textual Test Fixtures

Reusable pytest fixtures for efficient Textual application testing.

Quick Reference

# conftest.py
import pytest
from typing import AsyncIterator

@pytest.fixture
async def app_pilot() -> AsyncIterator[tuple[MyApp, Pilot]]:
    """Provide app with pilot for testing."""
    app = MyApp()
    async with app.run_test() as pilot:
        yield app, pilot

pytest Configuration

# pyproject.toml
[tool.pytest.ini_options]
asyncio_mode = "auto"  # No @pytest.mark.asyncio needed
testpaths = ["tests"]

Core Fixture Patterns

1. App Factory Fixture

Create app instances with pilot access:

@pytest.fixture
async def calculator_app() -> AsyncIterator[tuple[CalculatorApp, Pilot]]:
    """Provide calculator app with pilot."""
    app = CalculatorApp()
    async with app.run_test() as pilot:
        yield app, pilot

async def test_addition(calculator_app):
    app, pilot = calculator_app
    await pilot.press(*"2+2", "enter")
    await pilot.pause()
    assert app.query_one("#result").renderable == "4"

2. Parametrized App Factory

Support multiple app configurations:

@pytest.fixture
async def app_with_config(request) -> AsyncIterator[tuple[MyApp, Pilot]]:
    """Parametrized app fixture."""
    config = getattr(request, "param", {})
    app = MyApp(**config)
    async with app.run_test() as pilot:
        yield app, pilot

@pytest.mark.parametrize("app_with_config", [
    {"theme": "dark"},
    {"theme": "light"},
], indirect=True)
async def test_themed_app(app_with_config):
    app, pilot = app_with_config
    # Test with different themes

3. Custom Terminal Size Fixture

Test responsive layouts:

@pytest.fixture
async def large_terminal() -> AsyncIterator[tuple[MyApp, Pilot]]:
    """App with large terminal for testing sidebar visibility."""
    app = MyApp()
    async with app.run_test(size=(120, 40)) as pilot:
        yield app, pilot

@pytest.fixture
async def small_terminal() -> AsyncIterator[tuple[MyApp, Pilot]]:
    """App with small terminal for testing compact layout."""
    app = MyApp()
    async with app.run_test(size=(60, 20)) as pilot:
        yield app, pilot

4. Snapshot Fixture with Common Setup

Disable animations for stable snapshots:

@pytest.fixture
def snap_compare_stable(snap_compare):
    """snap_compare with animations disabled."""
    def wrapper(app, **kwargs):
        original_run_before = kwargs.get("run_before")

        async def run_before(pilot):
            # Disable animations
            for widget in pilot.app.query("*"):
                widget.can_animate = False
            # Run user's setup
            if original_run_before:
                await original_run_before(pilot)

        kwargs["run_before"] = run_before
        return snap_compare(app, **kwargs)
    return wrapper

def test_stable_snapshot(snap_compare_stable):
    assert snap_compare_stable(MyApp())

Mock Fixtures

Mock API Client

from unittest.mock import AsyncMock, patch

@pytest.fixture
def mock_api():
    """Mock external API calls."""
    with patch("myapp.api.fetch_data", new_callable=AsyncMock) as mock:
        mock.return_value = {"users": [{"name": "Alice"}]}
        yield mock

async def test_data_loading(app_pilot, mock_api):
    app, pilot = app_pilot
    await pilot.press("r")  # Trigger refresh
    await pilot.app.workers.wait_for_complete()

    mock_api.assert_called_once()
    assert len(app.query(".user-item")) == 1

Mock Database

from unittest.mock import MagicMock

@pytest.fixture
def mock_db():
    """Mock database connection."""
    mock = MagicMock()
    mock.query.return_value = [
        {"id": 1, "name": "Task 1"},
        {"id": 2, "name": "Task 2"},
    ]
    with patch("myapp.db.get_connection", return_value=mock):
        yield mock

Mock Time (Stable Timestamps)

from unittest.mock import patch
from datetime import datetime

@pytest.fixture
def frozen_time():
    """Freeze time for deterministic tests."""
    fixed = datetime(2025, 1, 1, 12, 0, 0)
    with patch("myapp.datetime") as mock_dt:
        mock_dt.now.return_value = fixed
        mock_dt.side_effect = lambda *args, **kw: datetime(*args, **kw)
        yield fixed

Mock Environment Variables

import os
from unittest.mock import patch

@pytest.fixture
def mock_env():
    """Set test environment variables."""
    env = {
        "API_KEY": "test-key",
        "DEBUG": "true",
    }
    with patch.dict(os.environ, env):
        yield env

conftest.py Organization

# tests/conftest.py
"""Shared fixtures for all tests."""

import pytest
from typing import AsyncIterator
from unittest.mock import AsyncMock, patch

from myapp import MyApp
from textual.pilot import Pilot


# === App Fixtures ===

@pytest.fixture
async def app_pilot() -> AsyncIterator[tuple[MyApp, Pilot]]:
    """Standard app with pilot."""
    app = MyApp()
    async with app.run_test() as pilot:
        yield app, pilot


@pytest.fixture
async def app_large() -> AsyncIterator[tuple[MyApp, Pilot]]:
    """App with large terminal."""
    app = MyApp()
    async with app.run_test(size=(120, 40)) as pilot:
        yield app, pilot


# === Mock Fixtures ===

@pytest.fixture
def mock_api():
    """Mock API client."""
    with patch("myapp.api.client", new_callable=AsyncMock) as mock:
        yield mock


@pytest.fixture
def mock_settings():
    """Mock settings/config."""
    with patch("myapp.settings") as mock:
        mock.debug = True
        mock.api_url = "http://test"
        yield mock


# === Snapshot Fixtures ===

@pytest.fixture
def snap_compare_stable(snap_compare):
    """Snapshot comparison with animations disabled."""
    def wrapper(app, **kwargs):
        async def setup(pilot):
            for w in pilot.app.query("*"):
                w.can_animate = False
        kwargs.setdefault("run_before", setup)
        return snap_compare(app, **kwargs)
    return wrapper

Test File Organization

tests/
├── conftest.py              # Shared fixtures
├── unit/
│   ├── conftest.py          # Unit-specific fixtures
│   ├── test_widgets.py
│   └── test_models.py
├── integration/
│   ├── conftest.py          # Integration-specific fixtures
│   └── test_workflows.py
└── snapshot/
    ├── conftest.py          # Snapshot-specific fixtures
    ├── test_layouts.py
    └── __snapshots__/       # Committed SVG baselines

Advanced Patterns

Fixture Composition

@pytest.fixture
async def authenticated_app(app_pilot, mock_api):
    """App with authenticated user."""
    app, pilot = app_pilot
    mock_api.login.return_value = {"token": "test-token"}

    # Perform login
    await pilot.press(*"testuser", "tab", *"password", "enter")
    await pilot.pause()

    return app, pilot

Async Context Manager Fixture

from contextlib import asynccontextmanager

@asynccontextmanager
async def app_context(config=None):
    """Reusable app context manager."""
    app = MyApp(**(config or {}))
    async with app.run_test() as pilot:
        yield app, pilot

@pytest.fixture
async def default_app():
    async with app_context() as (app, pilot):
        yield app, pilot

@pytest.fixture
async def debug_app():
    async with app_context({"debug": True}) as (app, pilot):
        yield app, pilot

Common Pitfalls

| Pitfall | Solution | |---------|----------| | Fixture not async | Use async def for fixtures using run_test() | | Missing yield | Use yield not return in async context fixtures | | Fixture scope wrong | Default to function scope for Textual apps | | Mock not cleaned up | Use context managers (with patch(...)) |

textual-test-fixtures