Nealepetrillo Claude Skills Pytest Pytest

Pytest

Fixture Patterns

Scopes

function (default) > class > module > package > session

Higher scopes execute first. Teardown in reverse order. Dynamic scope via callable:

@pytest.fixture(scope=lambda fixture_name, config: "session" if config.getoption("--reuse") else "function")

Yield Fixtures (preferred teardown)

@pytest.fixture
def db_conn():
    conn = create_connection()
    yield conn           # test runs here
    conn.close()         # teardown

Factory Fixtures

@pytest.fixture
def make_user(db):
    created = []
    def _make(name, role="user"):
        u = User(name=name, role=role)
        db.add(u)
        created.append(u)
        return u
    yield _make
    for u in created:
        db.delete(u)

Autouse

@pytest.fixture(autouse=True)
def reset_env(monkeypatch):
    monkeypatch.delenv("API_KEY", raising=False)

Parametrized Fixtures

@pytest.fixture(params=["sqlite", "postgres"], ids=["sqlite", "pg"])
def db(request):
    return connect(request.param)

Override Hierarchy

conftest.py fixtures override parent directory. Module-level overrides conftest.

Request Introspection

@pytest.fixture
def data(request):
    marker = request.node.get_closest_marker("data_file")
    if marker:
        return load(marker.args[0])

Parametrization

Basic

@pytest.mark.parametrize("input,expected", [("3+5", 8), ("2+4", 6)])
def test_eval(input, expected):
    assert eval(input) == expected

Cartesian Product (stacked decorators)

@pytest.mark.parametrize("x", [0, 1])
@pytest.mark.parametrize("y", [2, 3])
def test_foo(x, y): ...  # 4 tests

With Marks and IDs

@pytest.mark.parametrize("val,expected", [
    pytest.param("ok", True, id="happy-path"),
    pytest.param("", False, marks=pytest.mark.xfail, id="empty"),
])

Indirect (route through fixture)

@pytest.mark.parametrize("db", ["sqlite", "pg"], indirect=True)
def test_query(db): ...

Dynamic via Hook

def pytest_generate_tests(metafunc):
    if "db" in metafunc.fixturenames:
        metafunc.parametrize("db", get_db_configs(), indirect=True)

Assertions

Exception Testing

with pytest.raises(ValueError, match=r"invalid.*input"):
    do_something()

# With custom validation (v8.4+)
with pytest.raises(APIError, check=lambda e: e.status == 404):
    api.get("/missing")

Floating Point

assert 0.1 + 0.2 == pytest.approx(0.3)
assert result == pytest.approx(expected, rel=1e-3)

Warnings

with pytest.warns(DeprecationWarning, match="old_func"):
    old_func()

Custom Assertion Helpers

def assert_valid_response(resp, status=200):
    __tracebackhide__ = True  # hide from traceback
    assert resp.status_code == status
    assert resp.json() is not None

Skip & XFail

@pytest.mark.skip(reason="not implemented")
@pytest.mark.skipif(sys.platform == "win32", reason="unix only")
@pytest.mark.xfail(reason="known bug", strict=True)  # strict: xpass = FAIL

pytest.importorskip("pandas", minversion="2.0")
pytest.skip("reason", allow_module_level=True)  # skip entire module

Markers

Register to avoid warnings and enable --strict-markers:

[tool.pytest.ini_options]
markers = ["slow: slow tests", "integration: integration tests"]

Select: pytest -m "not slow", pytest -m "slow and integration"

Monkeypatch Quick Reference

monkeypatch.setattr("module.func", mock_func)
monkeypatch.setattr(obj, "attr", value)
monkeypatch.setenv("KEY", "val")
monkeypatch.delenv("KEY", raising=False)
monkeypatch.setitem(dict_obj, "key", "val")
monkeypatch.syspath_prepend("/path")
monkeypatch.chdir("/tmp")

Output & Debugging

pytest -v                    # verbose test names
pytest -vv                   # verbose + detailed diffs
pytest -x                    # stop on first failure
pytest --maxfail=3           # stop after 3 failures
pytest --pdb                 # debugger on failure
pytest --tb=short            # short tracebacks
pytest -r fEs                # summary: failed, Errors, skipped
pytest --durations=10        # 10 slowest tests
pytest -s                    # disable capture (see prints)
pytest --lf                  # rerun last failures
pytest --sw                  # stepwise mode

Plugin Selection Guide

Need parallel execution? → See plugin-xdist.md

• -n auto for CPU parallelism, --dist=loadscope to keep module tests together

Need mocking?

• Simple patching → use built-in monkeypatch fixture
• Call tracking/spies/stubs → See plugin-mock.md (pytest-mock)
• Record/replay → See plugin-mock.md (pytest-automock)

Need async testing? → See plugin-asyncio.md

• Config: asyncio_mode = "auto" for zero-decorator async tests

Need browser testing? → See plugin-playwright.md

• Sync: pytest-playwright, Async: pytest-playwright-asyncio

Need database fixtures? → See plugin-postgresql.md

• Factory pattern with load for schema, postgresql_noproc for Docker/CI

Need something else? → See plugin-catalog.md

• 1,745+ official plugins organized by category

Other deep plugins → See plugin-misc.md

• pytest-stub, pytest-tmp-files, pytest-venv, pytest-bigquery-mock, pytest-bg-process

Configuration Quick Start

# pyproject.toml
[tool.pytest.ini_options]
addopts = "-ra -q --strict-markers --import-mode=importlib"
testpaths = ["tests"]
markers = ["slow: slow tests", "integration: integration tests"]
filterwarnings = ["error", "ignore::DeprecationWarning"]
log_cli = true
log_cli_level = "INFO"

Config precedence: pytest.toml / .pytest.toml > pytest.ini / .pytest.ini > pyproject.toml > tox.ini > setup.cfg

For full config options → See configuration.md

Reference Files

• api-reference.md -- API signatures, markers, hooks, exit codes, collection tree
• configuration.md -- Config files, all INI options, all CLI flags, env vars
• fixtures-reference.md -- Built-in fixtures: capture, logging, monkeypatch, tmp_path, cache, pytester
• advanced-patterns.md -- Plugin dev, hook writing, custom collection, unittest compat, CI, import modes
• plugin-catalog.md -- 1,745+ plugins organized by category
• plugin-xdist.md -- Parallel execution, distribution modes, worker management
• plugin-mock.md -- pytest-mock (mocker fixture, spy, stub) + pytest-automock
• plugin-asyncio.md -- Async testing, modes, event loop scope
• plugin-playwright.md -- Browser testing (sync + async), fixtures, config
• plugin-postgresql.md -- PostgreSQL fixtures, factories, Docker, SQLAlchemy
• plugin-misc.md -- stub, tmp-files, venv, bigquery-mock, bg-process

Source: nealepetrillo/claude-skills-pytest — distributed by TomeVault.