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Write and evaluate effective Python tests using pytest. Use when writing tests, reviewing test code, debugging test failures, or improving test coverage. Covers test design, fixtures, parameterization, mocking, and async testing.
npx skill4agent add eyh0602/skillshub testing-python# Good: Name tells you what's broken
def test_user_creation_sets_defaults():
user = User(name="Alice")
assert user.role == "member"
assert user.id is not None
assert user.created_at is not None
# Bad: If this fails, what behavior is broken?
def test_user():
user = User(name="Alice")
assert user.role == "member"
user.promote()
assert user.role == "admin"
assert user.can_delete_others()import pytest
@pytest.mark.parametrize("input,expected", [
("hello", "HELLO"),
("World", "WORLD"),
("", ""),
("123", "123"),
])
def test_uppercase_conversion(input, expected):
assert input.upper() == expectedasyncio_mode = "auto"# Correct
async def test_async_operation():
result = await some_async_function()
assert result == expected
# Wrong - don't add this
@pytest.mark.asyncio
async def test_async_operation():
...# Correct
import pytest
from fastmcp import FastMCP
from fastmcp.client import Client
async def test_something():
mcp = FastMCP("test")
...
# Wrong - no local imports
async def test_something():
from fastmcp import FastMCP # Don't do this
...from fastmcp import FastMCP
from fastmcp.client import Client
mcp = FastMCP("TestServer")
@mcp.tool
def greet(name: str) -> str:
return f"Hello, {name}!"
async def test_greet_tool():
async with Client(mcp) as client:
result = await client.call_tool("greet", {"name": "World"})
assert result[0].text == "Hello, World!"inline-snapshotfrom inline_snapshot import snapshot
def test_schema_generation():
schema = generate_schema(MyModel)
assert schema == snapshot() # Will auto-populate on first runpytest --inline-snapshot=createpytest --inline-snapshot=fix@pytest.fixture
def client():
return Client()
async def test_with_client(client):
result = await client.ping()
assert result is not Nonetmp_pathdef test_file_writing(tmp_path):
file = tmp_path / "test.txt"
file.write_text("content")
assert file.read_text() == "content"from unittest.mock import patch, AsyncMock
async def test_external_api_call():
with patch("mymodule.external_client.fetch", new_callable=AsyncMock) as mock:
mock.return_value = {"data": "test"}
result = await my_function()
assert result == {"data": "test"}# Good
def test_login_fails_with_invalid_password():
def test_user_can_update_own_profile():
def test_admin_can_delete_any_user():
# Bad
def test_login():
def test_update():
def test_delete():import pytest
def test_raises_on_invalid_input():
with pytest.raises(ValueError, match="must be positive"):
calculate(-1)
async def test_async_raises():
with pytest.raises(ConnectionError):
await connect_to_invalid_host()uv run pytest -n auto # Run all tests in parallel
uv run pytest -n auto -x # Stop on first failure
uv run pytest path/to/test.py # Run specific file
uv run pytest -k "test_name" # Run tests matching pattern
uv run pytest -m "not integration" # Exclude integration tests@pytest.mark.asyncio