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Published: Mar 14, 2016 License: MIT, MIT Imports: 3 Imported by: 0


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Clock is a small library for mocking time in Go. It provides an interface around the standard library's time package so that the application can use the realtime clock while tests can use the mock clock.


Realtime Clock

Your application can maintain a Clock variable that will allow realtime and mock clocks to be interchangable. For example, if you had an Application type:

import ""

type Application struct {
	Clock clock.Clock

You could initialize it to use the realtime clock like this:

var app Application
app.Clock = clock.New()

Then all timers and time-related functionality should be performed from the Clock variable.

Mocking time

In your tests, you will want to use a Mock clock:

import (


func TestApplication_DoSomething(t *testing.T) {
	mock := clock.NewMock()
	app := Application{Clock: mock}

Now that you've initialized your application to use the mock clock, you can adjust the time programmatically. The mock clock always starts from the Unix epoch (midnight, Jan 1, 1970 UTC).

Controlling time

The mock clock provides the same functions that the standard library's time package provides. For example, to find the current time, you use the Now() function:

mock := clock.NewMock()

// Find the current time.
mock.Now().UTC() // 1970-01-01 00:00:00 +0000 UTC

// Move the clock forward.
mock.Add(2 * time.Hour)

// Check the time again. It's 2 hours later!
mock.Now().UTC() // 1970-01-01 02:00:00 +0000 UTC

Timers and Tickers are also controlled by this same mock clock. They will only execute when the clock is moved forward:

mock := clock.NewMock()
count := 0

// Kick off a timer to increment every 1 mock second.
go func() {
    ticker := clock.Ticker(1 * time.Second)
    for {

// Move the clock forward 10 second.
mock.Add(10 * time.Second)

// This prints 10.




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type Clock

type Clock interface {
	After(d time.Duration) <-chan time.Time
	AfterFunc(d time.Duration, f func()) *Timer
	Now() time.Time
	Sleep(d time.Duration)
	Tick(d time.Duration) <-chan time.Time
	Ticker(d time.Duration) *Ticker
	Timer(d time.Duration) *Timer

Clock represents an interface to the functions in the standard library time package. Two implementations are available in the clock package. The first is a real-time clock which simply wraps the time package's functions. The second is a mock clock which will only make forward progress when programmatically adjusted.

func New

func New() Clock

New returns an instance of a real-time clock.

type Mock

type Mock struct {
	// contains filtered or unexported fields

Mock represents a mock clock that only moves forward programmically. It can be preferable to a real-time clock when testing time-based functionality.

func NewMock

func NewMock() *Mock

NewMock returns an instance of a mock clock. The current time of the mock clock on initialization is the Unix epoch.

func (*Mock) Add

func (m *Mock) Add(d time.Duration)

Add moves the current time of the mock clock forward by the duration. This should only be called from a single goroutine at a time.

func (*Mock) After

func (m *Mock) After(d time.Duration) <-chan time.Time

After waits for the duration to elapse and then sends the current time on the returned channel.

func (*Mock) AfterFunc

func (m *Mock) AfterFunc(d time.Duration, f func()) *Timer

AfterFunc waits for the duration to elapse and then executes a function. A Timer is returned that can be stopped.

func (*Mock) Now

func (m *Mock) Now() time.Time

Now returns the current wall time on the mock clock.

func (*Mock) Set

func (m *Mock) Set(t time.Time)

Sets the current time of the mock clock to a specific one. This should only be called from a single goroutine at a time.

func (*Mock) Sleep

func (m *Mock) Sleep(d time.Duration)

Sleep pauses the goroutine for the given duration on the mock clock. The clock must be moved forward in a separate goroutine.

func (*Mock) Tick

func (m *Mock) Tick(d time.Duration) <-chan time.Time

Tick is a convenience function for Ticker(). It will return a ticker channel that cannot be stopped.

func (*Mock) Ticker

func (m *Mock) Ticker(d time.Duration) *Ticker

Ticker creates a new instance of Ticker.

func (*Mock) Timer

func (m *Mock) Timer(d time.Duration) *Timer

Timer creates a new instance of Timer.

type Ticker

type Ticker struct {
	C <-chan time.Time
	// contains filtered or unexported fields

Ticker holds a channel that receives "ticks" at regular intervals.

func (*Ticker) Stop

func (t *Ticker) Stop()

Stop turns off the ticker.

type Timer

type Timer struct {
	C <-chan time.Time
	// contains filtered or unexported fields

Timer represents a single event. The current time will be sent on C, unless the timer was created by AfterFunc.

func (*Timer) Reset

func (t *Timer) Reset(d time.Duration) bool

Reset changes the expiry time of the timer

func (*Timer) Stop

func (t *Timer) Stop() bool

Stop turns off the ticker.

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