Mocking Timers #

To make your tests faster, you can mock calls to setTimeout and setInterval. All methods to manipulate timers are located on vi object that you can import from vitest package or access globally, if you have global config enabled.

useFakeTimers #

Type: () => Vitest

To enable mocking timers, you need to call this method. It will wrap all further calls to timers, until vi.useRealTimers() is called.

useRealTimers #

Type: () => Vitest

When timers are run out, you may call this method to return mocked timers to its original implementations. All timers that were run before will not be restored.

runOnlyPendingTimers #

Type: () => Vitest

This method will call every timer that was initiated after vi.useFakeTimers() call. It will not fire any timer that was initiated during its call. For example this will only log 1:

let i = 0
setInterval(() => console.log(++i), 50)

vi.runOnlyPendingTimers()

runAllTimers #

Type: () => Vitest

This method will invoke every initiated timer until the timers queue is empty. It means that every timer called during runAllTimers will be fired. If you have an infinite interval, it will throw after 10 000 tries. For example this will log 1, 2, 3:

let i = 0
setTimeout(() => console.log(++i))
let interval = setInterval(() => {
    console.log(++i)
    if (i === 2) {
        clearInterval(interval)
    }
}, 50)

vi.runAllTimers()

advanceTimersByTime #

Type: (ms: number) => Vitest

Works just like runAllTimers, but will end after passed milliseconds. For example this will log 1, 2, 3 and will not throw:

let i = 0
setInterval(() => console.log(++i), 50)

vi.advanceTimersByTime(150)

advanceTimersToNextTimer #

Type: () => Vitest

Will call next available timer. Useful to make assertions between each timer call. You can chain call it to manage timers by yourself.

let i = 0
setInterval(() => console.log(++i), 50)

vi.advanceTimersToNextTimer() // log 1
  .advanceTimersToNextTimer() // log 2
  .advanceTimersToNextTimer() // log 3