Plugin adoption proposal: pytest-do-not-mock — enforce "no mocks" contracts in tests

[LifeLex]

TL;DR

I maintain pytest-do-not-mock, a small pytest plugin that lets authors mark tests as "no mocks allowed" (globally, or for specific functions) and fails the test if unittest.mock is used to violate that contract. I'd like to propose moving it under the pytest-dev GitHub organization for shared maintenance and discoverability, and I'm looking for feedback from the maintainers on whether the idea and the implementation are a good fit.

Motivation

The plugin is a direct response to Increase Test Fidelity By Avoiding Mocks (Google Testing Blog, Feb 2024) and the "Test Doubles" chapter of Software Engineering at Google. The short version of the argument those sources make:

Prefer the real implementation, then a fake, then a mock — in that order. Mocks are the lowest-fidelity option and the most likely to drift from production behavior.
In practice, once unittest.mock is available, that preference order inverts — mocks become the default because they're the easiest option. Reviews catch some of this, but "please don't mock the payment processor here" is a convention, not an enforceable rule. This plugin turns that convention into an assertion that runs in CI.

What it does

Two usage modes, both opt-in via the standard @pytest.mark mechanism:

import pytest

# Block-all mode: no mocking whatsoever
@pytest.mark.do_not_mock
def test_payment_integration():
    # any Mock/MagicMock/AsyncMock/patch/patch.object/patch.dict/
    # create_autospec in this test raises DoNotMockError
    ...

# Targeted mode: protect specific functions
@pytest.mark.do_not_mock(protect=process_payment)
def test_selective():
    # only patches targeting process_payment are blocked;
    # everything else is free to be mocked
    with patch("myapp.send_email"):
        ...

# String paths work as positional args
@pytest.mark.do_not_mock("myapp.payments.charge")
def test_with_path():
    ...

• No-args mode: blocks all unittest.mock construction and patching for the duration of that test.
• Targeted mode: accepts function references (via protect=) or string paths (positional args) and only blocks patch/patch.object aimed at those targets. Other mocking is untouched.
• Class and module scope: @pytest.mark.do_not_mock on a class applies to all methods. pytestmark = pytest.mark.do_not_mock applies to an entire module.

Violations raise DoNotMockError with a message pointing at the offending call, so the failure is actionable without digging through tracebacks.

Why it could be a good fit for pytest-dev

• Scope is narrow and stable. It's not trying to replace pytest-mock or unittest.mock
• Idiomatic pytest. Uses @pytest.mark, iter_markers, and hookwrapper — no custom decorators or namespace injection. Markers stack across function/class/module scope; the plugin walks every do_not_mock marker on the item and unions them, with a bare marker at any scope winning over targeted inner markers.
• No new runtime dependencies beyond pytest>=7.0.
• Fills a gap.

Current state

• Python 3.10–3.13, tested via tox.
• ruff, mypy --strict, and pyright --strict all green.
• Pre-commit hooks, GitHub Actions CI, PyPI trusted publishing set up.
• MIT licensed.
• Published on PyPI as pytest-do-not-mock (0.1.x, beta).
• Project structure is small on purpose (~5 modules under src/pytest_do_not_mock/).
  Links:
• Repo: https://github.com/LifeLex/pytest-do-not-mock
• PyPI: https://pypi.org/project/pytest-do-not-mock/
• Readme with the full "when to use / when not to use" section: https://github.com/LifeLex/pytest-do-not-mock#readme

What I'm asking for

1. Feedback on the idea itself does this belong as a pytest-dev plugin, or is it better left as a community/third-party plugin? I'd rather hear "no, and here's why" than push something that doesn't fit.
2. Feedback on scope and API specifically the two-mode decorator design, the set of unittest.mock entry points it intercepts, and DoNotMockError as the failure mode. Happy to change any of it.
3. If there's interest, the transfer itself moving the GitHub repo to pytest-dev/pytest-do-not-mock, handing over PyPI maintainer rights, and following whatever the org's contribution/release conventions are.

[RonnyPfannschmidt]

I like the idea itself

Markers and hooks should be used instead of the decorators that returns a wrapper

[LifeLex]

I am happy to change the decorator to a marker, is that always the preference for pytest plugins ? Just want to know for the future

[RonnyPfannschmidt]

The marker preference ensures test functions stay unmodified

Markers already are correctly typed in addition

[LifeLex]

Thank you, I am about to merge a PR that will make use of markers instead of the decorators, I've also updated the description of this discussion

[RonnyPfannschmidt]

Consider iter_markers so class and module level markers are taken into account as well

[LifeLex]

Good catch, I will raise a PR today to cover that, thank you ! 😄