Crate mock_instant

mock_instant

NOTE As of version 0.4, the thread-local clock has been removed. The clock will always be thread-safe.

To ensure unsurprising behavior, reset the clock before each test (if that behavior is applicable.)

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This crate allows you to test Instant/Duration/SystemTime code, deterministically.

This uses a static mutex to have a thread-aware clock.

It provides a replacement std::time::Instant that uses a deterministic ‘clock’

You can swap out the std::time::Instant with this one by doing something similar to:

#[cfg(test)]
use mock_instant::Instant;

#[cfg(not(test))]
use std::time::Instant;

or for a std::time::SystemTime

#[cfg(test)]
use mock_instant::{SystemTime, SystemTimeError};

#[cfg(not(test))]
use std::time::{SystemTime, SystemTimeError};

Or a std::time::SystemTime with this one by doing something similar to:

#[cfg(test)]
use mock_instant::SystemTime;

#[cfg(not(test))]
use std::time::SystemTime;

Example

use std::time::Duration;

let now = Instant::now();
MockClock::advance(Duration::from_secs(15));
MockClock::advance(Duration::from_secs(2));

// its been '17' seconds
assert_eq!(now.elapsed(), Duration::from_secs(17));

API:

// Overrides the current time to this `Duration`
MockClick::set_time(time: Duration)

// Advance the current time by this `Duration`
MockClick::advance(time: Duration)

// Get the current time
MockClick::time() -> Duration

// Overrides the current `SystemTime` to this duration
MockClick::set_system_time(time: Duration)

// Advance the current `SystemTime` by this duration
MockClick::sdvance_system_time(time: Duration)

// Get the current `SystemTime`
MockClick::system_time() -> Duration

Usage:

NOTE The clock starts at Duration::ZERO

In your tests, you can use MockClock::set_time(Duration::ZERO) to reset the clock back to 0. Or, you can set it to some sentinel time value.

Then, before you check your time-based logic, you can advance the clock by some Duration (it’ll freeze the time to that duration)

You can also get the current frozen time with MockClock::time

SystemTime is also mockable with a similar API.

Structs

• Instant
  A simple deterministic Instant wrapped around a modifiable Duration
• MockClock
  A Mock clock
• SystemTime
  A simple deterministic SystemTime wrapped around a modifiable Duration
• SystemTimeError
  An error returned from the duration_since and elapsed methods on SystemTime, used to learn how far in the opposite direction a system time lies.

Constants

• UNIX_EPOCH
  A mocked UNIX_EPOCH. This starts at 0 rather than the traditional unix epoch date.