Kill metrics-counter and install_patch gate mutation survivors (#27, #28)

[leynos]

Closes #27, #28.

Summary

Second of two survivor-triage PRs following the 2026-07-10 mutmut 3.6.0
run on main @ 03b8ed1. Stacked on #32 (branch
kill-mutation-survivors); it kills the 61 survivors that PR
explicitly deferred:

• exact get_metrics() counter assertions across every dispatch and
  resolve _record_metric call site, pinning both the precise counter
  key and the increment (Mutation testing: metrics counter survivors #27);
• install_patch version-gate coverage — the major-version boundaries,
  the mixed supported/unsupported combination that pins the or
  operator, missing __version__ defaults, and strict-mode message
  content — plus _validate_astroid_shape logger routing, exact error
  messages, missing-attribute handling, and signature tolerance (Mutation testing: install_patch version-gate and shape-validation survivors #28).

Tests only; no production code changes.

Before/after survivor counts

State	Mutants	Killed	Outstanding (survived + no tests)
main @ 03b8ed1 (baseline)	621	381	240
Base PR (kill-mutation-survivors)	407	346	61
This PR (full mutmut run)	407	407	0

Two mutants the triage worklist had recorded as equivalent (the "0"
version-default strings in install_patch) are killed here instead of
annotated: asserting the exact skip-warning message
(pylint 0, astroid 0) distinguishes them.

Review walkthrough

• tests/test_patch_helpers.py
  is the only file touched:
  • exact-Counter assertions added to the existing resolve, dispatch
    routing, and non-string-dir-entry tests, so every
    _record_metric key is pinned via the public get_metrics()
    snapshot (Mutation testing: metrics counter survivors #27);
  • new tests for the class-child cached/built counters, the const
    special/plain counters, and the dummy getattr-failure counter
    (Mutation testing: metrics counter survivors #27);
  • test_install_patch_version_gate_reports_exact_versions
    parametrizes the unsupported combinations (pylint 5.x, astroid 5.x,
    and both __version__ attributes missing) and asserts the exact
    warning message (Mutation testing: install_patch version-gate and shape-validation survivors #28);
  • strict-mode and _validate_astroid_shape tests assert exact
    PatchError and log-record content, that errors land on the
    caller-supplied logger, that a missing object_build still raises
    PatchError, and that extra trailing parameters are tolerated
    (Mutation testing: install_patch version-gate and shape-validation survivors #28).

Red-green evidence

_patch module (hand-applied metric mutant,
_record_metric("dispatch.routine") → _record_metric(None)):

=== RED: apply _patch.x__dispatch_member_to_child metric mutant ===
FAILED tests/test_patch_helpers.py::test_dispatch_member_to_child_routes_routines
1 failed in 0.49s
=== GREEN: revert ===
1 passed in 0.13s

Validation

• ruff format --check, ruff check, ty check pkg tests tools, and
  pytest -n auto (91 passed, 1 skipped) all pass on this branch.
• Full uv run mutmut run at this branch's tree: 407 generated,
  407 killed, 0 survived, 0 timeouts, 0 suspicious.

🤖 Generated with Claude Code

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📥 Commits

Reviewing files that changed from the base of the PR and between 845a5b2 and 6b94e98.

📒 Files selected for processing (1)

• tests/test_patch_helpers.py

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---

Summary

• Added comprehensive tests for get_metrics() counters across dispatch, caching, resolution, descriptors, routines, module-like members, and dummy fallbacks, addressing #27.
• Expanded coverage for install_patch version gates, strict-mode logging, AST-shape validation, logger routing, exact errors, missing attributes, and tolerant signatures, addressing #28.
• Mutation testing kills all 407 generated mutants, with no survivors or timeouts.
• Formatting, linting, type checks, and tests pass: 91 passed and 1 skipped.

Walkthrough

The test suite now verifies patch-helper metric counters, cached versus rebuilt children, dummy fallbacks, version-gate messages, strict errors, logger propagation, AST-shape validation, and acceptance of extra trailing parameters.

Changes

Patch helper coverage

Layer / File(s)	Summary
Resolution and dispatch metric assertions tests/test_patch_helpers.py	Assert counters for bound-method unwrapping, successful and failed resolution, descriptor and routine dispatch, module-like dispatch, and non-string directory entries.
Child-build and fallback metrics tests/test_patch_helpers.py	Distinguish cached and rebuilt class children, special and normal constant dispatch, and dummy getattr-failure recording.
Installation gates and shape validation tests/test_patch_helpers.py	Verify exact version-related warnings and errors, caller logger usage, builder validation failures, signature reporting, and extra trailing parameters.

Possibly related issues

• Issue 28 — The tests cover its version-gate, logging, strict-mode, missing-version, and extra-parameter objectives.

Suggested labels: Issue

Poem

Count every route and name every gate,
Let logs speak clearly and errors translate.
Cache what is cached, build what is new,
Validate shapes as signatures pass through.
Tests march brightly, metric bells ring.

🚥 Pre-merge checks | ✅ 19 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The PR also adds install_patch and AST-shape tests tied to #28, which are outside the only linked issue #27.	Split the #28 test coverage into a separate PR, or add #28 to the linked issues if it is intended to be in scope.

✅ Passed checks (19 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately reflects the survivor-triage test work and includes the linked issue references.
Description check	✅ Passed	The description is directly about the same test-only survivor-triage changes and their issue references.
Linked Issues check	✅ Passed	The PR covers the metrics-counter survivors required by #27, including exact keys and increments for the listed paths.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Testing (Overall)	✅ Passed	Approve: the new tests hit real routing, public metric counters, version-gate messages, and logger routing; they fail on plausible regressions.
User-Facing Documentation	✅ Passed	PASS: Only tests changed; no user-facing functionality or behaviour was added, so docs/users-guide.md needed no update.
Developer Documentation	✅ Passed	Only test comments changed; no internal API, architecture, tooling, or build requirements changed, and the developers' guide already covers _patch.py, install_patch, get_metrics, and build steps.
Module-Level Documentation	✅ Passed	PASS: the only changed module, tests/test_patch_helpers.py, has a clear top-level docstring, and the repo-wide scan found docstrings on all Python modules.
Testing (Unit And Behavioural)	✅ Passed	Accept it: the PR adds boundary tests for install_patch/object_build and unit tests for metrics, edge cases, and error paths; no E2E gap appears.
Testing (Property / Proof)	✅ Passed	The PR only adds concrete regression tests for finite branches; no new broad invariant or proof obligation calls for extra property/proof tooling.
Testing (Compile-Time / Ui)	✅ Passed	No Rust/TypeScript compile-time surface exists here; the PR only adds focused Python assertions, so trybuild or snapshots are not required.
Unit Architecture	✅ Passed	PASS: Side effects and fallibility stay explicit at the command/validation boundary; the branch adds tests and no-op logging/typing refactors, not hidden state or conflated responsibilities.
Domain Architecture	✅ Passed	PASS: the branch changes only tests, and they probe patch-helper boundary behaviour without altering domain code or leaking new infrastructure concerns.
Observability	✅ Passed	PASS: this PR is test-only plus no-op pragma/comment changes; it does not alter production observability, and existing logs/counters were already in place.
Security And Privacy	✅ Passed	Tests only; they add no secrets, auth gaps, injection sinks, or broadened permissions, and the logged/versioned values are fake or dependency metadata.
Performance And Resource Use	✅ Passed	Approve it: only tests changed, and the added loops, Hypothesis cases, and thread pools are small, bounded, and CI-only.
Concurrency And State	✅ Passed	Only test comments changed; no shared mutable state, locking, async, or ordering semantics were altered.
Architectural Complexity And Maintainability	✅ Passed	Approve it: the PR stays in one test file and adds only local test fixtures; the NamedTuple/helper cut argument noise instead of adding a new layer.
Rust Compiler Lint Integrity	✅ Passed	Only tests/test_patch_helpers.py changed; no Rust sources, lint suppressions, or clone-related edits were introduced.

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• Create stacked PR
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• Create PR with unit tests
• Commit unit tests in branch kill-mutation-survivor-metrics-gates

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Reviewer's Guide

Adds precise metrics Counter assertions and new coverage around _patch dispatch/resolve flows plus detailed install_patch version-gate and astroid shape validation behavior, all in tests only.

File-Level Changes

Change	Details	Files
Assert exact metrics Counter contents for resolve/dispatch paths and add focused metrics tests to pin every _record_metric counter key/increment behavior.	Augment existing resolve-member tests with full Counter equality checks covering bound-method unwraps, successful resolves, getattr failures, and non-string dir-entry handling. Extend dispatch-member tests to assert per-path metric increments for method descriptors, data descriptors, routines, module-like members, imported members, and builder object_build calls. Add new tests for _build_class_child to distinguish cached vs built members via separate class dispatch counters. Add new tests for _build_const_child to distinguish special attributes from ordinary const builds via separate const dispatch counters. Add an object-build test that drives a getattr failure path and asserts the dummy getattr-failure dispatch metric is incremented.	tests/test_patch_helpers.py
Expand install_patch and astroid shape-validation tests to lock down exact messages, logger routing, and version/signature handling semantics.	Add helper to simulate PyPy environment with specific/missing pylint and astroid version values, used across new version-gate tests. Parametrize install_patch version-gate tests over unsupported and missing-version combinations, asserting exact warning messages including the reported versions and that the patch is not installed. Add strict-mode test asserting PatchError is raised with the exact skip message and that the same message is logged at ERROR level. Add install_patch test verifying shape-validation errors are logged through a caller-supplied logger and that object_build is left untouched when validation fails. Add _validate_astroid_shape tests for missing InspectBuilder, non-callable object_build, completely missing object_build, unsupported signatures (including logged signature detail), and accepted signatures with extra trailing parameters.	tests/test_patch_helpers.py

Possibly linked issues

• Mutation testing: metrics counter survivors #27: PR adds exact get_metrics Counter assertions and new tests for each dispatch/resolve metric named in the issue.
• Mutation testing: install_patch version-gate and shape-validation survivors #28: PR’s new install_patch and _validate_astroid_shape tests implement the issue’s suggested cases, killing those mutation survivors.

---

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[leynos]

Review finding actioned (branch rebased onto the updated #32):

• CodeScene — Excess Number of Function Arguments (test_install_patch_version_gate_reports_exact_versions): the parametrized version scenarios are now expressed as a _VersionGateCase named tuple, reducing the test to (monkeypatch, caplog, case).

A full mutmut run at the new tip still reports 407 generated / 407 killed / 0 survived.

[leynos]

Heads-up: #34 replaced ci.yml's bespoke cs-coverage upload step (which CodeScene rejects on pull-request branches) with the shared generate-coverage action, and the CS_ACCESS_TOKEN secret is now set repo-wide. This branch's head still carries the old ci.yml, so its next CI run would execute the old upload step and fail. Please rebase onto (or merge) main before pushing further changes.

[codescene-access]

No quality gates enabled for this code.

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