test(metrics): add coverage for metrics timing decorator

[mnadzam]

Closes #978

[coderabbitai]

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• tests/test_metrics.py

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• tests/test_metrics.py

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📝 Walkthrough

Walkthrough

Adds tests/tests_metrics.py (new) which provides pytest coverage for fromager.metrics. It defines several functions decorated with @metrics.timeit to exercise timing storage and descriptions on a provided context.WorkContext, asserting that timing entries are written to tmp_context.time_store only when both a requirement and a resolvable version source exist (explicit version arg or Version in the return). Tests verify descriptions stored in tmp_context.time_description_store, that original return values are preserved, that exceptions propagate without writing timing data, that metrics.summarize() logs expected INFO output when data exists and none when empty, and unit-tests _extract_version_from_return() across None, Version, tuples, and non-iterable inputs.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~15 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the primary change: adding pytest coverage for the metrics timing decorator.
Description check	✅ Passed	The description references issue #978, which directly relates to the PR's objective of adding test coverage for metrics.py.
Linked Issues check	✅ Passed	The PR implements all four acceptance criteria from #978: timeit() timing storage, timeit() exception propagation, summarize() logging, and _extract_version_from_return() behavior across variants.
Out of Scope Changes check	✅ Passed	All changes are scoped to test coverage for metrics.py as required; no unrelated modifications to source code or other modules detected.

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@tests/test_metrics.py`:
- Around line 128-144: Add a new unit test in tests/test_metrics.py that calls
metrics._extract_version_from_return(None) and asserts it returns None to cover
the acceptance criterion for issue `#978`; ensure the test function name is unique
(e.g., test_extract_version_none) and follows the same style as the other tests
so it runs with the existing test suite and exercises the code path where
iterating over None would raise a TypeError.
- Around line 31-37: The helper function _test_raises used under the
metrics.timeit decorator must accept a version parameter so the decorator's
storage path (which only runs when both req and version are present) can be
exercised; update the _test_raises signature to include version: str | None =
None (or the project's Version type if different) and ensure the function
accepts and ignores this parameter while still raising the RuntimeError so the
test can pass a version and verify that exceptions prevent storage.

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• tests/test_metrics.py