by benbjohnson

benbjohnson / clock

Clock is a small library for mocking time in Go.

244 Stars 58 Forks Last release: 5 months ago (v1.0.3) MIT License 36 Commits 4 Releases

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Clock is a small library for mocking time in Go. It provides an interface around the standard library's

package so that the application can use the realtime clock while tests can use the mock clock.


Realtime Clock

Your application can maintain a

variable that will allow realtime and mock clocks to be interchangeable. For example, if you had an
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


Mocking time

In your tests, you will want to use a

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 UTC on Jan 1, 1970).

Controlling time

The mock clock provides the same functions that the standard library's

package provides. For example, to find the current time, you use the
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 {

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