How to test the current time with Go (I made a very thin library)

What kind of article?

I wondered what to do with Golang for tests involving the current time. I didn't get it right, so I made a library with only the functions I wanted.

What I checked

@ tomtwinkle's article: [Golang] Create a testable current time acquisition process introduced the following three methods.

• monkey.Patch
• flextime package
• Route in context

In addition, Kentaro Kawano's material was also helpful.

• clock package
• External injection

But, I hope it's easier like this. .. ..

What I made

I thought, I made a very thin library. https://github.com/bubusuke/xtime

Thoughts

It's the same as trying to do flextime and clock. You can wrap and replace time.Now (). But these two weren't quite right for me.

flextime is a little worrisome because it is exclusively controlled. (Also described in this article) Also, flextime has a long name (I want to shorten the coding). clock is a little worrisome because the name is too different from time.

Feature

Name: Time-like, but let's make it a short name. → xtime Function: Aperture! → Only two. Just use xtime.Now (). ~~ At the time of testing, just change the time with xtime.Mock (value returned by $ {xtime.Now ()}). ~~ At the time of testing, just change the time with xtime.Mock (function executed by $ {xtime.Now ()}). How to use: You can use it by replacing the part that uses time.Now () in the existing source with this.

• ~ ~ Correction: 2021/01/16 After the first posting ~ ~ *
• Changed the argument of xtime.Mock from value to function for more flexibility. *
• Now you can create a Mock that advances the time for each execution as described in the test case, and you can reset the Mock. *

git is open to the public, but the source is also posted below.

Source

xtime.go

package xtime

import (
	"time"
)

var now func() time.Time = time.Now

// Mock overwrites return value of xtime.Now().
// You must not use this function except for in test.
func Mock(fn func() time.Time) {
	now = fn
}

// Now returns the value of time.Now().
// If the Mock function has been executed in advance, the value set by Mock is returned.
func Now() time.Time {
	return now()
}

test

xtime_test.go

package xtime_test

import (
	"testing"
	"time"
	"xtime"
)

type incrementalMock struct {
	i time.Duration
	t time.Time
}

func (m *incrementalMock) Now() time.Time {
	m.i++
	return m.t.Add(time.Second * m.i)
}

func TestNow(t *testing.T) {
	// case 1.
	// Default xtime.Now behavior
	// 'xtime.Now() == time.Now()' become false due to the μ second level execution time difference.
	if !(xtime.Now().Sub(time.Now()) <= time.Second*1) {
		t.Error("Default xtime.Now() must be same to time.Now().")
	}

	// case 2.
	// Constant value Mock
	mockTime := time.Date(2021, 1, 1, 0, 0, 0, 0, time.UTC)
	xtime.Mock(func() time.Time { return mockTime })
	if xtime.Now() != mockTime {
		t.Error("xtime.Now() must be same to MockTime.")
	}

	// case 3.
	// Incremental value Mock
	incMock := &incrementalMock{
		i: 0,
		t: mockTime,
	}
	xtime.Mock(incMock.Now)
	if xtime.Now().Sub(mockTime) != time.Second*1 {
		t.Error("xtime.Now() must be same to MockTime+1sec.")
	}
	if xtime.Now().Sub(mockTime) != time.Second*2 {
		t.Error("xtime.Now() must be same to MockTime+2sec.")
	}

	// case 4.
	// reset
	xtime.Mock(time.Now)
	// Same to 1st test case.
	if !(xtime.Now().Sub(time.Now()) <= time.Second*1) {
		t.Error("Default xtime.Now() must be same to time.Now().")
	}

}