fix: fix multiple bugs in _apply_deterministic_patches

[aseembits93]

Summary

• Re-entrancy guard: Added _DETERMINISTIC_PATCHES_APPLIED flag to prevent infinite recursion if pytest_configure runs twice
• Removed unnecessary original function calls: Every mock was calling the original function and discarding the result — unnecessary overhead and a failure point (e.g. uuid.uuid1() can raise on some platforms)
• Actually patch datetime.datetime.now/utcnow: Previous code stored mocks to builtins but never patched datetime.datetime. Now uses a DeterministicDatetime subclass. Also fixes now(tz=None) incorrectly returning tz-aware datetime
• Patch missing time functions: Added time_ns, monotonic, monotonic_ns (perf_counter_ns intentionally not patched — used by profiling infrastructure)
• Removed useless np.random.default_rng(42): Created a Generator and discarded it — no effect
• Removed redundant try/except around os.urandom: os is always available

Test plan

• uv run pytest tests/test_pytest_plugin_deterministic_patches.py -v — 23 tests pass
• uv run pytest tests/ -x --timeout=60 — 2645 passed, 0 failed
• uv run prek run --from-ref origin/main — ruff check + format pass

🤖 Generated with Claude Code

[claude]

Claude finished @aseembits93's task in 3m 40s —— View job

---

PR Review Summary

• Triage changed files
• Run prek lint/type checks
• Resolve stale review threads (none found)
• Code review
• Duplicate detection
• Test coverage analysis

---

Prek Checks

✅ ruff check and ruff format both pass.

Mypy Notes

Two new mypy errors introduced by this PR in _apply_deterministic_patches:

Line	Error	Status
175	now return type datetime.datetime incompatible with supertype's DeterministicDatetime — due to typeshed using TypeVar/Self for cls return type	Left alone (complex generic, changing behavior to fix)
181	Same for utcnow	Left alone
184	Cannot assign to a type for datetime.datetime = DeterministicDatetime	Left alone (inherent to monkey-patching approach)

Auto-fixed (committed): removed unused _ORIGINAL_MONOTONIC variable (captured _time_module.monotonic but never referenced anywhere in the file) and added missing tz: datetime.tzinfo | None = None type annotation to DeterministicDatetime.now.

Code Review

The fixes in this PR are correct and well-motivated. A few observations:

DeterministicDatetime.now patching limitation (pytest_plugin.py:173–185): The datetime.datetime = DeterministicDatetime assignment patches the datetime module's class attribute. Code that did from datetime import datetime before pytest_configure runs won't see the mock. This is a known limitation of subclass-based datetime patching, and it's an improvement over the old approach (which stored mock functions to builtins but never actually patched datetime.datetime at all). Worth noting in a comment for future maintainers. Fix this →

_DETERMINISTIC_PATCHES_APPLIED never reset (pytest_plugin.py:97): Patches are one-shot and permanent for the session lifetime — which is correct for a pytest plugin. However, if two test processes each load the plugin module fresh (which they do), the flag resets correctly per-process. No issue here.

perf_counter_ns exclusion rationale (pytest_plugin.py:157–158): The comment correctly explains the carve-out. Good.

mock_datetime_now tz bug fixed (pytest_plugin.py:176–179): The old code with tz=None returned the tz-aware fixed_datetime directly, so callers expecting a naive datetime would get surprising results. The new code correctly returns fixed_datetime.replace(tzinfo=None) for the naive case and fixed_datetime.astimezone(tz) for the aware case.

Duplicate Detection

No duplicates detected. The DeterministicDatetime subclass pattern is unique to pytest_plugin.py.

Test Coverage

All 23 tests pass. Coverage for pytest_plugin.py is 26% overall, which is expected — the bulk of the plugin's code runs through pytest hooks that require a full test session to exercise, not standalone unit tests. The deterministic-patches section (the main change in this PR) is well-covered by the test suite.

---

Last updated: 2026-03-12
| Branch

[codeflash-ai]

⚡️ Codeflash found optimizations for this PR

📄 13% (0.13x) speedup for _apply_deterministic_patches in codeflash/verification/pytest_plugin.py

⏱️ Runtime : 37.5 microseconds → 33.1 microseconds (best of 67 runs)

A new Optimization Review has been created.

🔗 Review here