clock: Index | Examples | Files

package clock

import ""

Package clock provides an abstraction for system time that enables testing of time-sensitive code.

Where you'd use time.Now, instead use clk.Now where clk is an instance of Clock.

When running your code in production, pass it a Clock given by Default() and when you're running it in your tests, pass it an instance of Clock from NewFake().

When you do that, you can use FakeClock's Add and Set methods to control how time behaves in your code making them more reliable while also expanding the space of problems you can test.

This code intentionally does not attempt to provide an abstraction over time.Ticker and time.Timer because Go does not have the runtime or API hooks available to do reliably. See

Be sure to test Time equality with time.Time#Equal, not ==.



Package Files

clock.go timer.go

type Clock Uses

type Clock interface {
    // Now returns the Clock's current view of the time. Mutating the
    // returned Time will not mutate the clock's time.
    Now() time.Time

    // Sleep causes the current goroutine to sleep for the given duration.

    // After returns a channel that fires after the given duration.
    After(time.Duration) <-chan time.Time

    // Since is a short hand for Now().Sub(t).
    Since(time.Time) time.Duration

    // NewTimer makes a Timer based on this clock's time. Using Timers and
    // negative durations in the Clock or Timer API is undefined behavior and
    // may be changed.
    NewTimer(time.Duration) *Timer

Clock is an abstraction over system time. New instances of it can be made with Default and NewFake.


c := New()
now := c.Now()



func Default Uses

func Default() Clock

Deprecated: Default is just an alias for New but less memorable.

func New Uses

func New() Clock

New returns a Clock that matches the actual system time.

type FakeClock Uses

type FakeClock interface {
    // Adjust the time that will be returned by Now.
    Add(d time.Duration)

    // Set the Clock's time to exactly the time given.
    Set(t time.Time)

FakeClock is a Clock with additional controls. The return value of Now return can be modified with Add. Use NewFake to get a thread-safe FakeClock implementation.


c := New()
fc := NewFake()
fc.Add(20 * time.Hour)
fc.Add(-5 * time.Minute) // negatives work, as well

if fc.Now().Equal(fc.Now()) {
    fmt.Println("FakeClocks' Times always equal themselves.")
if !c.Now().Equal(fc.Now()) {
    fmt.Println("Clock and FakeClock can be set to different times.")
if !fc.Now().Equal(NewFake().Now()) {
    fmt.Println("FakeClocks work independently, too.")


FakeClocks' Times always equal themselves.
Clock and FakeClock can be set to different times.
FakeClocks work independently, too.

func NewFake Uses

func NewFake() FakeClock

NewFake returns a FakeClock to be used in tests that need to manipulate time. Its initial value is always the unix epoch in the UTC timezone. The FakeClock returned is thread-safe.

type Timer Uses

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

func (*Timer) Reset Uses

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

func (*Timer) Stop Uses

func (t *Timer) Stop() bool

Package clock imports 3 packages (graph) and is imported by 590 packages. Updated 2018-11-04. Refresh now. Tools for package owners.