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Published: Apr 1, 2023 License: Apache-2.0 Imports: 4 Imported by: 2,112



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A simple fake clock for Go.


Replace uses of the time package with the clockwork.Clock interface instead.

For example, instead of using time.Sleep directly:

func myFunc() {
	time.Sleep(3 * time.Second)

Inject a clock and use its Sleep method instead:

func myFunc(clock clockwork.Clock) {
	clock.Sleep(3 * time.Second)

Now you can easily test myFunc with a FakeClock:

func TestMyFunc(t *testing.T) {
	c := clockwork.NewFakeClock()

	// Start our sleepy function
	var wg sync.WaitGroup
	go func() {

	// Ensure we wait until myFunc is sleeping


	// Advance the FakeClock forward in time
	c.Advance(3 * time.Second)

	// Wait until the function completes


and in production builds, simply inject the real clock instead:


See example_test.go for a full example.


clockwork is inspired by @wickman's threaded fake clock, and the Golang playground


Apache License, Version 2.0. Please see License File for more information.




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func AddToContext added in v0.2.3

func AddToContext(ctx context.Context, clock Clock) context.Context

AddToContext creates a derived context that references the specified clock.


type Clock

type Clock interface {
	After(d time.Duration) <-chan time.Time
	Sleep(d time.Duration)
	Now() time.Time
	Since(t time.Time) time.Duration
	NewTicker(d time.Duration) Ticker
	NewTimer(d time.Duration) Timer
	AfterFunc(d time.Duration, f func()) Timer

Clock provides an interface that packages can use instead of directly using the time module, so that chronology-related behavior can be tested.

func FromContext added in v0.2.3

func FromContext(ctx context.Context) Clock

FromContext extracts a clock from the context. If not present, a real clock is returned.

func NewRealClock

func NewRealClock() Clock

NewRealClock returns a Clock which simply delegates calls to the actual time package; it should be used by packages in production.

type FakeClock

type FakeClock interface {
	// Advance advances the FakeClock to a new point in time, ensuring any existing
	// waiters are notified appropriately before returning.
	Advance(d time.Duration)
	// BlockUntil blocks until the FakeClock has the given number of waiters.
	BlockUntil(waiters int)

FakeClock provides an interface for a clock which can be manually advanced through time.

FakeClock maintains a list of "waiters," which consists of all callers waiting on the underlying clock (i.e. Tickers and Timers including callers of Sleep or After). Users can call BlockUntil to block until the clock has an expected number of waiters.

func NewFakeClock

func NewFakeClock() FakeClock

NewFakeClock returns a FakeClock implementation which can be manually advanced through time for testing. The initial time of the FakeClock will be the current system time.

Tests that require a deterministic time must use NewFakeClockAt.

func NewFakeClockAt

func NewFakeClockAt(t time.Time) FakeClock

NewFakeClockAt returns a FakeClock initialised at the given time.Time.

type Ticker added in v0.2.0

type Ticker interface {
	Chan() <-chan time.Time
	Reset(d time.Duration)

Ticker provides an interface which can be used instead of directly using time.Ticker. The real-time ticker t provides ticks through t.C which becomes t.Chan() to make this channel requirement definable in this interface.

type Timer added in v0.3.0

type Timer interface {
	Chan() <-chan time.Time
	Reset(d time.Duration) bool
	Stop() bool

Timer provides an interface which can be used instead of directly using time.Timer. The real-time timer t provides events through t.C which becomes t.Chan() to make this channel requirement definable in this interface.

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