95 lines
3.0 KiB
Python
95 lines
3.0 KiB
Python
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"""Indirection for time functions.
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We intentionally grab some "time" functions internally to avoid tests mocking "time" to affect
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pytest runtime information (issue #185).
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Fixture "mock_timing" also interacts with this module for pytest's own tests.
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"""
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from __future__ import annotations
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import dataclasses
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from datetime import datetime
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from datetime import timezone
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from time import perf_counter
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from time import sleep
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from time import time
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from typing import TYPE_CHECKING
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if TYPE_CHECKING:
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from pytest import MonkeyPatch
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@dataclasses.dataclass(frozen=True)
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class Instant:
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"""
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Represents an instant in time, used to both get the timestamp value and to measure
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the duration of a time span.
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Inspired by Rust's `std::time::Instant`.
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"""
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# Creation time of this instant, using time.time(), to measure actual time.
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# Note: using a `lambda` to correctly get the mocked time via `MockTiming`.
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time: float = dataclasses.field(default_factory=lambda: time(), init=False)
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# Performance counter tick of the instant, used to measure precise elapsed time.
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# Note: using a `lambda` to correctly get the mocked time via `MockTiming`.
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perf_count: float = dataclasses.field(
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default_factory=lambda: perf_counter(), init=False
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)
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def elapsed(self) -> Duration:
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"""Measure the duration since `Instant` was created."""
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return Duration(start=self, stop=Instant())
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def as_utc(self) -> datetime:
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"""Instant as UTC datetime."""
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return datetime.fromtimestamp(self.time, timezone.utc)
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@dataclasses.dataclass(frozen=True)
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class Duration:
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"""A span of time as measured by `Instant.elapsed()`."""
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start: Instant
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stop: Instant
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@property
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def seconds(self) -> float:
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"""Elapsed time of the duration in seconds, measured using a performance counter for precise timing."""
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return self.stop.perf_count - self.start.perf_count
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@dataclasses.dataclass
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class MockTiming:
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"""Mocks _pytest.timing with a known object that can be used to control timing in tests
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deterministically.
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pytest itself should always use functions from `_pytest.timing` instead of `time` directly.
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This then allows us more control over time during testing, if testing code also
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uses `_pytest.timing` functions.
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Time is static, and only advances through `sleep` calls, thus tests might sleep over large
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numbers and obtain accurate time() calls at the end, making tests reliable and instant."""
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_current_time: float = datetime(2020, 5, 22, 14, 20, 50).timestamp()
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def sleep(self, seconds: float) -> None:
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self._current_time += seconds
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def time(self) -> float:
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return self._current_time
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def patch(self, monkeypatch: MonkeyPatch) -> None:
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from _pytest import timing # noqa: PLW0406
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monkeypatch.setattr(timing, "sleep", self.sleep)
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monkeypatch.setattr(timing, "time", self.time)
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monkeypatch.setattr(timing, "perf_counter", self.time)
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__all__ = ["perf_counter", "sleep", "time"]
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