test(tick): improve mutation coverage - #695
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Add focused boundary and state-transition tests for clock, delay, periodic timer, fast instant, and timer internals. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
martinhavelka (wukchung)
approved these changes
Aug 26, 2026
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Pull request overview
This PR adds targeted tests across the tick crate to increase mutation coverage by exercising boundary conditions and state transitions in timer driving, clock configuration, and internal time sources.
Changes:
- Added new unit tests for timer ordering/discriminator behavior and timer-advancement edge cases.
- Added tests for clock-control auto-advance behavior, delay overflow normalization, and periodic timer exact-deadline firing.
- Introduced a small
#[cfg(test)]introspection helper onSimpleClockto validate fast-instant configuration in tests.
Reviewed changes
Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.
Show a summary per file
| File | Description |
|---|---|
| crates/tick/src/timers.rs | Adds tests for discriminator sequencing and a 1ns boundary in advance_timers. |
| crates/tick/src/state.rs | Adds a clone/uniqueness test for shared timer storage. |
| crates/tick/src/simple_clock.rs | Adds a test-only helper to check whether fast instant mode is active. |
| crates/tick/src/periodic_timer.rs | Adds a test asserting firing at an exact deadline when driven by ClockControl. |
| crates/tick/src/fast_instant.rs | Strengthens the platform clock read test (but currently in a potentially flaky way). |
| crates/tick/src/delay.rs | Adds a test intended to cover overflow behavior in timer registration. |
| crates/tick/src/clock.rs | Extends fast-instant configuration test assertions via SimpleClock helper. |
| crates/tick/src/clock_control.rs | Adds tests for auto-advance-timers evaluation and limit consumption. |
Suppressed comments (1)
crates/tick/src/timers.rs:175
- This test reaches into
timers.wakersand constructs aTimerKeywithdiscriminator = 0, which is not reachable viaTimers::register(it starts at 1). Using the public registration path keeps the test aligned with real behavior and reduces coupling to internals.
let next = now + Duration::from_nanos(1);
let key = TimerKey::new(next, 0);
timers.wakers.insert(key, Waker::noop().clone());
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Evgenii (Vaiz)
approved these changes
Aug 26, 2026
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #695 +/- ##
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Coverage 100.0% 100.0%
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Files 559 559
Lines 60774 60777 +3
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+ Hits 60774 60777 +3
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Pull request overview
Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.
Suppressed comments (2)
crates/tick/src/timers.rs:165
- This test hard-codes the initial discriminator values (1 and 2), which makes it brittle to internal changes that don’t affect the intended property (that discriminators progress sequentially). Prefer asserting the relationship between the two keys (wrapping increment) rather than exact starting values.
let first = timers.register(when, Waker::noop().clone());
let second = timers.register(when, Waker::noop().clone());
assert_eq!(first.discriminator, 1);
assert_eq!(second.discriminator, 2);
crates/tick/src/fast_instant.rs:126
platform_time()is not guaranteed to be non-zero (e.g., very early after boot it can legitimately return 0), so asserting!= Duration::ZEROcan be flaky. Consider waiting briefly and retrying a bounded number of times, then asserting the value became non-zero to keep the mutant-killing intent without relying on a single sample.
fn platform_time_can_be_read() {
assert_ne!(platform_time(), Duration::ZERO);
Comment on lines
+171
to
+175
| let now = Instant::now(); | ||
| let next = now + Duration::from_nanos(1); | ||
| let key = TimerKey::new(next, 0); | ||
| timers.wakers.insert(key, Waker::noop().clone()); | ||
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Comment on lines
+214
to
+216
| #[test] | ||
| fn overflowing_reregistration_clears_existing_timer() { | ||
| let clock = Clock::new_system_frozen(); |
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Add focused boundary and state-transition tests for clock, delay, periodic timer, fast instant, and timer internals.