In golang, Time.Format() removes trailing zeros from fractional part

Question

How can I prevent go's Time.Format() from removing trailing zeros from fractional part? I have following unit tests that fails.

package main

import (
    "testing"
    "time"
)

func TestTimeFormatting(t *testing.T) {
    timestamp := time.Date(2017, 1,2, 3, 4, 5, 600000*1000, time.UTC)
    timestamp_string := timestamp.Format("2006-01-02T15:04:05.999-07:00")
    expected := "2017-01-02T03:04:05.600+00:00"

    if expected != timestamp_string {
        t.Errorf("Invalid timestamp formating, expected %v, got %v", expected, timestamp_string)
    }
}

Output:

$ go test
--- FAIL: TestTimeFormatting (0.00s)
    main_test.go:14: Invalid timestamp formating, expected 2017-01-02T03:04:05.600+00:00, got 2017-01-02T03:04:05.6+00:00
FAIL
exit status 1
FAIL    _/home/sasa/Bugs/go-formatter   0.001s

Any idea how to solve this?

Answer 1

Ah, is was there in documentation. One should use 000 instead of 999 if you want to keep zeros.

package main

import (
    "testing"
    "time"
)

func TestTimeFormatting(t *testing.T) {
    timestamp := time.Date(2017, 1,2, 3, 4, 5, 600000*1000, time.UTC)
    timestamp_string := timestamp.Format("2006-01-02T15:04:05.000-07:00")
    expected := "2017-01-02T03:04:05.600+00:00"

    if expected != timestamp_string {
        t.Errorf("Invalid timestamp formating, expected %v, got %v", expected, timestamp_string)
    }
}