# Nealepetrillo Claude Skills Pytest Pytest

> Pytest

- Skill: `tomevault-io/nealepetrillo-claude-skills-pytest-pytest` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/nealepetrillo-claude-skills-pytest-pytest`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/nealepetrillo-claude-skills-pytest-pytest/raw
- Safety review: pending (external: skill-scanner WARNING, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/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:
```python
@pytest.fixture(scope=lambda fixture_name, config: "session" if config.getoption("--reuse") else "function")
```

### Yield Fixtures (preferred teardown)
```python
@pytest.fixture
def db_conn():
    conn = create_connection()
    yield conn           # test runs here
    conn.close()         # teardown
```

### Factory Fixtures
```python
@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
```python
@pytest.fixture(autouse=True)
def reset_env(monkeypatch):
    monkeypatch.delenv("API_KEY", raising=False)
```

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

## Parametrization

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

### Cartesian Product (stacked decorators)
```python
@pytest.mark.parametrize("x", [0, 1])
@pytest.mark.parametrize("y", [2, 3])
def test_foo(x, y): ...  # 4 tests
```

### With Marks and IDs
```python
@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)
```python
@pytest.mark.parametrize("db", ["sqlite", "pg"], indirect=True)
def test_query(db): ...
```

### Dynamic via Hook
```python
def pytest_generate_tests(metafunc):
    if "db" in metafunc.fixturenames:
        metafunc.parametrize("db", get_db_configs(), indirect=True)
```

## Assertions

### Exception Testing
```python
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
```python
assert 0.1 + 0.2 == pytest.approx(0.3)
assert result == pytest.approx(expected, rel=1e-3)
```

### Warnings
```python
with pytest.warns(DeprecationWarning, match="old_func"):
    old_func()
```

### Custom Assertion Helpers
```python
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

```python
@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`:
```toml
[tool.pytest.ini_options]
markers = ["slow: slow tests", "integration: integration tests"]
```

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

## Monkeypatch Quick Reference

```python
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](references/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](references/plugin-mock.md) (pytest-mock)
- Record/replay → See [plugin-mock.md](references/plugin-mock.md) (pytest-automock)

**Need async testing?** → See [plugin-asyncio.md](references/plugin-asyncio.md)
- Config: `asyncio_mode = "auto"` for zero-decorator async tests

**Need browser testing?** → See [plugin-playwright.md](references/plugin-playwright.md)
- Sync: pytest-playwright, Async: pytest-playwright-asyncio

**Need database fixtures?** → See [plugin-postgresql.md](references/plugin-postgresql.md)
- Factory pattern with `load` for schema, `postgresql_noproc` for Docker/CI

**Need something else?** → See [plugin-catalog.md](references/plugin-catalog.md)
- 1,745+ official plugins organized by category

**Other deep plugins** → See [plugin-misc.md](references/plugin-misc.md)
- pytest-stub, pytest-tmp-files, pytest-venv, pytest-bigquery-mock, pytest-bg-process

## Configuration Quick Start

```toml
# 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](references/configuration.md)

## Reference Files

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

---
> Source: [nealepetrillo/claude-skills-pytest](https://github.com/nealepetrillo/claude-skills-pytest) — distributed by [TomeVault](https://tomevault.io).
<!-- tomevault:4.0:skill_md:2026-06-16 -->