Crate mock_instant

mock_instant

NOTE As of version 0.5. MockClock/Instant/SystemTime have been moved to specific modules

NOTE The modules, global and thread_local change the behavior across threads. If global is used, the clock keeps its state across threads, otherwise if thread_local is used, a new source is made for each thread

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

---

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

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::global::Instant;

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

or for a std::time::SystemTime

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

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

use mock_instant::global::{MockClock, Instant};
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`
MockClock::set_time(time: Duration)

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

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

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

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

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

// Determine if this MockClock was thread-local: (useful for assertions to ensure the right mode is being used)
MockClock::is_thread_local() -> bool
Instant::now().is_thread_local() -> bool
SystemTime::now().is_thread_local() -> bool

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.

Thread-safety:

Two modes are provided via modules. The APIs are identical but the MockClock source has different behavior in different threads.

• mock_instant::global

  • MockClock will have a new state per thread
  • Instantwill have a new state per thread
  • SystemTime will have a new state per thread

• mock_instant::thread_local

  • MockClock will have a new state per thread
  • Instantwill have a new state per thread
  • SystemTime will have a new state per thread

Modules

• global
  Global state.
• thread_local
  Thread-local state.

Structs

• 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.