#Fake timers

The fake timers may be useful when a piece of code sets a long timeout that we don't want to wait for in a test.

Rstest provides some utility functions to help you fake timers powered by @sinonjs/fake-timers.

#rstest.useFakeTimers

• Type: (config?: FakeTimerInstallOpts) => Rstest

To enable mocking timers, you need to call this method. It uses @sinonjs/fake-timers under the hood.

rstest.useFakeTimers();

You can also pass a configuration object to customize the behavior of the fake timers.

#rstest.useRealTimers

• Type: () => Rstest

Restores the original timer functions (such as setTimeout, setInterval, etc.), disabling the fake timers.

rstest.useRealTimers();

#rstest.isFakeTimers

• Type: () => boolean

Returns true if fake timers are currently enabled, otherwise false.

if (rstest.isFakeTimers()) {
  // Fake timers are active
}

#rstest.setSystemTime

• Type: (now?: number | Date) => Rstest

Sets the current system time used by fake timers. Useful for testing code that depends on the current date or time.

rstest.useFakeTimers();
rstest.setSystemTime(new Date('2020-01-01T00:00:00Z'));

#rstest.getRealSystemTime

• Type: () => number

Returns the real system time (as a timestamp), even when fake timers are enabled.

const realTime = rstest.getRealSystemTime();

#rstest.runAllTicks

• Type: () => Rstest

Runs all queued microtasks (e.g., process.nextTick).

#rstest.runAllTimers

• Type: () => Rstest

Executes all pending timers (both timeouts and intervals).

#rstest.runAllTimersAsync

• Type: () => Promise<Rstest>

Asynchronously executes all pending timers.

#rstest.runOnlyPendingTimers

• Type: () => Rstest

Runs only the currently pending timers (does not schedule new ones).

#rstest.runOnlyPendingTimersAsync

• Type: () => Promise<Rstest>

Asynchronously runs only the currently pending timers.

#rstest.advanceTimersByTime

• Type: (ms: number) => Rstest

Advances the fake timers by the specified milliseconds, executing any timers scheduled within that time.

#rstest.advanceTimersByTimeAsync

• Type: (ms: number) => Promise<Rstest>

Asynchronously advances the fake timers by the specified milliseconds.

#rstest.advanceTimersToNextTimer

• Type: (steps?: number) => Rstest

Advances the timers to the next scheduled timer, optionally for a given number of steps.

#rstest.advanceTimersToNextTimerAsync

• Type: (steps?: number) => Promise<Rstest>

Asynchronously advances the timers to the next scheduled timer.

#rstest.advanceTimersToNextFrame

• Type: () => Rstest

Advances the timers to the next animation frame.

#rstest.getTimerCount

• Type: () => number

Returns the number of fake timers still left to run.

const count = rstest.getTimerCount();

#rstest.clearAllTimers

• Type: () => Rstest

Removes all timers that are scheduled to run.

rstest.clearAllTimers();