indexes.go

package main

import (
	"errors"
	"fmt"
	"time"
)

func main() {
	startDate := time.Date(2017, 06, 21, 10, 19, 00, 0, time.UTC)
	endDate := time.Date(2017, 06, 23, 11, 00, 00, 0, time.UTC)
	fmt.Println(GetIndexes(startDate, endDate))
}

func GetIndexes(startDate, endDate time.Time) ([]string, error) {
	if endDate.Before(startDate) {
		return nil, errors.New("Invalid date range")
	}
	ret := make([]string, 0, 0)
	for t := startDate; t.Before(endDate); t = t.AddDate(0, 0, 1) {
		ret = append(ret,
			fmt.Sprintf("logstash-%d.%02d.%02d", t.Year(), t.Month(), t.Day()))
	}
	return ret, nil
}

indexes_test.go

package main

import (
	"testing"
	"time"

	. "gopkg.in/check.v1"
)

func Test(t *testing.T) { TestingT(t) }

type MySuite struct{}

var _ = Suite(&MySuite{})

func (s *MySuite) TestGetIndexes(c *C) {
	startDate := time.Date(2017, 06, 21, 10, 19, 00, 0, time.UTC)
	endDate := time.Date(2017, 06, 23, 11, 00, 00, 0, time.UTC)
	expected := []string{"logstash-2017.06.21", "logstash-2017.06.22", "logstash-2017.06.23"}

	indexes, err := GetIndexes(startDate, endDate)

	c.Assert(err, IsNil)
	c.Assert(indexes, DeepEquals, expected)
}