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Kentaro Kawano

1. The document discusses various techniques for testing functions in Go that depend on the time.Now() function, including overriding time.Now(), using a fake clock interface, and monkey patching. 2. It provides examples of overriding time.Now() directly, using a fakeclock.FakeClock type from the clock package to inject a test clock, and monkey patching time.Now() using the monkey package. 3. The techniques allow isolating tests by faking the system time so time-dependent code returns predictable outputs for different test cases.

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Go 2017/07/07 Umeda.go #2
? (@kawaken) ? ? LINE ? Go 3 ? goa
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func CanDeliver() bool { hour := time.Now().Hour() // 8 20 return 8 <= hour && hour <= 20 } func
? 8 20 : true ? 21 7 : false
func TestCanDeliver(t *testing.T) { hour := time.Now().Hour() expected := 8 <= hour && hour <= 20 // result := CanDeliver() if expected == result { t.Log("OK") } else { t.Fatal("NG") } }
? time.Now ?
? ? ? ? ? 2 29
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1. 2. 3.
1.
func CanDeliver(hour int) bool { // 8 20 return 8 <= hour && hour <= 20 } time.Now
func TestCanDeliver(t *testing.T) { cases := []struct { hour int want bool }{ {7, false}, {8, true}, {20, true}, {21, false}, } for _, c := range cases { got := CanDeliver(c.hour) if got != c.want { t.Errorf("CanDeliver(%d) => %t, want %t", c.hour, got, c.want) } } }
2.
var now = time.Now // time.Now now func CanDeliver() bool { hour := now().Hour() // now // 8 20 return 8 <= hour && hour <= 20 } now
func fakeHour(hour int) { // time.Time func now now = func() time.Time { return time.Date(2017, 7, 7, hour, 0, 0, 0, time.Local) } } func TestCanDeliver(t *testing.T) { // snip... for _, c := range cases { fakeHour(c.hour) // fakeHour got := CanDeliver() if got != c.want { t.Errorf("hour: %d, CanDeliver() => %t, want %t", c.hour, got, c.want) } } now = time.Now // reset time }
3.
code.cloudfoundry.org/clock ? time ? ? clock/fakeclock/FakeClock
var myClock = clock.NewClock() // myClock clock.Clock func CanDeliver() bool { hour := myClock.Now().Hour() // myClock // 8 20 return 8 <= hour && hour <= 20 } myClock
func fakeHour(hour int) { // FakeClock myClock = fakeclock.NewFakeClock(time.Date(2017, 7, 7, hour, 0, 0, 0, time.Local)) } func TestCanDeliver(t *testing.T) { // snip... for _, c := range cases { fakeHour(c.hour) // fakeHour got := CanDeliver() if got != c.want { t.Errorf("hour: %d, CanDeliver() => %t, want %t", c.hour, got, c.want) } } myClock = clock.NewClock() // reset time }
? ? time.Now ? ? time.Now
time.Now
4.
func CanDeliver(hour int) bool { // 8 20 return 8 <= hour && hour <= 20 } func CanDeliverNow() bool { hour := time.Now().Hour() return CanDeliver(hour) }
5. Monkey patch
github.com/bouk/monkey ? Go ? ?
func CanDeliver() bool { hour := time.Now().Hour() // 8 20 return 8 <= hour && hour <= 20 }
func fakeHour(hour int) { // time.Now func monkey.Patch( time.Now, func() time.Time { return time.Date(2017, 7, 7, hour, 0, 0, 0, time.Local) }, ) } func TestCanDeliver(t *testing.T) { // snip... for _, c := range cases { fakeHour(c.hour) // fakeHour got := CanDeliver() if got != c.want { t.Errorf("hour: %d, CanDeliver() => %t, want %t", c.hour, got, c.want) } } monkey.Unpatch(time.Now) // reset time }
6. time
// time.Now func Now() Time { sec, nsec := now() return Time{sec + unixToInternal, nsec, Local} }
Now
/* src/time/time.go */ var fakeTime Time // func Fake(t Time) { fakeTime = t } func ResetFake() { fakeTime = Time{} } func Now() Time { if !fakeTime.IsZero() { return fakeTime } sec, nsec := now() return Time{sec + unixToInternal, nsec, Local} }
func CanDeliver() bool { hour := time.Now().Hour() // 8 20 return 8 <= hour && hour <= 20 }
func fakeHour(hour int) { time.Fake(time.Date(2017, 7, 7, hour, 0, 0, 0, time.Local)) } func TestCanDeliver(t *testing.T) { // snip... for _, c := range cases { fakeHour(c.hour) // fakeHour got := CanDeliver() if got != c.want { t.Errorf("hour: %d, CanDeliver() => %t, want %t", c.hour, got, c.want) } } time.ResetFake() // reset time }
% /usr/local/go1.8.3_faketime/bin/go test -v ./timepkg === RUN TestCanDeliver --- PASS: TestCanDeliver (0.00s) sample_test.go:22: 2017-07-07 07:00:00 +0900 JST sample_test.go:22: 2017-07-07 08:00:00 +0900 JST sample_test.go:22: 2017-07-07 20:00:00 +0900 JST sample_test.go:22: 2017-07-07 21:00:00 +0900 JST PASS ok github.com/kawaken/golang-time-testing/timepkg 0.466s
1. 2. code.cloudfoundry.org/clock 3. monkey

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  • 4. func CanDeliver() bool { hour := time.Now().Hour() // 8 20 return 8 <= hour && hour <= 20 } func
  • 5. ? 8 20 : true ? 21 7 : false
  • 6. func TestCanDeliver(t *testing.T) { hour := time.Now().Hour() expected := 8 <= hour && hour <= 20 // result := CanDeliver() if expected == result { t.Log("OK") } else { t.Fatal("NG") } }
  • 11. 1.
  • 12. func CanDeliver(hour int) bool { // 8 20 return 8 <= hour && hour <= 20 } time.Now
  • 13. func TestCanDeliver(t *testing.T) { cases := []struct { hour int want bool }{ {7, false}, {8, true}, {20, true}, {21, false}, } for _, c := range cases { got := CanDeliver(c.hour) if got != c.want { t.Errorf("CanDeliver(%d) => %t, want %t", c.hour, got, c.want) } } }
  • 14. 2.
  • 15. var now = time.Now // time.Now now func CanDeliver() bool { hour := now().Hour() // now // 8 20 return 8 <= hour && hour <= 20 } now
  • 16. func fakeHour(hour int) { // time.Time func now now = func() time.Time { return time.Date(2017, 7, 7, hour, 0, 0, 0, time.Local) } } func TestCanDeliver(t *testing.T) { // snip... for _, c := range cases { fakeHour(c.hour) // fakeHour got := CanDeliver() if got != c.want { t.Errorf("hour: %d, CanDeliver() => %t, want %t", c.hour, got, c.want) } } now = time.Now // reset time }
  • 17. 3.
  • 19. var myClock = clock.NewClock() // myClock clock.Clock func CanDeliver() bool { hour := myClock.Now().Hour() // myClock // 8 20 return 8 <= hour && hour <= 20 } myClock
  • 20. func fakeHour(hour int) { // FakeClock myClock = fakeclock.NewFakeClock(time.Date(2017, 7, 7, hour, 0, 0, 0, time.Local)) } func TestCanDeliver(t *testing.T) { // snip... for _, c := range cases { fakeHour(c.hour) // fakeHour got := CanDeliver() if got != c.want { t.Errorf("hour: %d, CanDeliver() => %t, want %t", c.hour, got, c.want) } } myClock = clock.NewClock() // reset time }
  • 23. 4.
  • 24. func CanDeliver(hour int) bool { // 8 20 return 8 <= hour && hour <= 20 } func CanDeliverNow() bool { hour := time.Now().Hour() return CanDeliver(hour) }
  • 27. func CanDeliver() bool { hour := time.Now().Hour() // 8 20 return 8 <= hour && hour <= 20 }
  • 28. func fakeHour(hour int) { // time.Now func monkey.Patch( time.Now, func() time.Time { return time.Date(2017, 7, 7, hour, 0, 0, 0, time.Local) }, ) } func TestCanDeliver(t *testing.T) { // snip... for _, c := range cases { fakeHour(c.hour) // fakeHour got := CanDeliver() if got != c.want { t.Errorf("hour: %d, CanDeliver() => %t, want %t", c.hour, got, c.want) } } monkey.Unpatch(time.Now) // reset time }
  • 30. // time.Now func Now() Time { sec, nsec := now() return Time{sec + unixToInternal, nsec, Local} }
  • 31. Now
  • 32. /* src/time/time.go */ var fakeTime Time // func Fake(t Time) { fakeTime = t } func ResetFake() { fakeTime = Time{} } func Now() Time { if !fakeTime.IsZero() { return fakeTime } sec, nsec := now() return Time{sec + unixToInternal, nsec, Local} }
  • 33. func CanDeliver() bool { hour := time.Now().Hour() // 8 20 return 8 <= hour && hour <= 20 }
  • 34. func fakeHour(hour int) { time.Fake(time.Date(2017, 7, 7, hour, 0, 0, 0, time.Local)) } func TestCanDeliver(t *testing.T) { // snip... for _, c := range cases { fakeHour(c.hour) // fakeHour got := CanDeliver() if got != c.want { t.Errorf("hour: %d, CanDeliver() => %t, want %t", c.hour, got, c.want) } } time.ResetFake() // reset time }
  • 35. % /usr/local/go1.8.3_faketime/bin/go test -v ./timepkg === RUN TestCanDeliver --- PASS: TestCanDeliver (0.00s) sample_test.go:22: 2017-07-07 07:00:00 +0900 JST sample_test.go:22: 2017-07-07 08:00:00 +0900 JST sample_test.go:22: 2017-07-07 20:00:00 +0900 JST sample_test.go:22: 2017-07-07 21:00:00 +0900 JST PASS ok github.com/kawaken/golang-time-testing/timepkg 0.466s