creating a new slice in several job options because appending modifies original (#809)

* creating a new slice in several job options because appending modifies original

* add tests

Author: JohnRoesler

Diff for: job.go

@@ -311,8 +311,7 @@ type Weekdays func() []time.Weekday
 // NewWeekdays provide the days of the week the job should run.
 func NewWeekdays(weekday time.Weekday, weekdays ...time.Weekday) Weekdays {
 	return func() []time.Weekday {
-		weekdays = append(weekdays, weekday)
-		return weekdays
+		return append([]time.Weekday{weekday}, weekdays...)
 	}
 }
 
@@ -400,8 +399,7 @@ type DaysOfTheMonth func() days
 //	-5 == 5 days before the end of the month.
 func NewDaysOfTheMonth(day int, moreDays ...int) DaysOfTheMonth {
 	return func() days {
-		moreDays = append(moreDays, day)
-		return moreDays
+		return append([]int{day}, moreDays...)
 	}
 }
 
@@ -439,8 +437,7 @@ type AtTimes func() []AtTime
 // the job should be run
 func NewAtTimes(atTime AtTime, atTimes ...AtTime) AtTimes {
 	return func() []AtTime {
-		atTimes = append(atTimes, atTime)
-		return atTimes
+		return append([]AtTime{atTime}, atTimes...)
 	}
 }
 

Diff for: job_test.go

@@ -724,3 +724,59 @@ func TestTimeFromAtTime(t *testing.T) {
 		})
 	}
 }
+
+func TestNewAtTimes(t *testing.T) {
+	at := NewAtTimes(
+		NewAtTime(1, 1, 1),
+		NewAtTime(2, 2, 2),
+	)
+
+	var times []string
+	for _, att := range at() {
+		timeStr := TimeFromAtTime(att, time.UTC).Format("15:04")
+		times = append(times, timeStr)
+	}
+
+	var timesAgain []string
+	for _, att := range at() {
+		timeStr := TimeFromAtTime(att, time.UTC).Format("15:04")
+		timesAgain = append(timesAgain, timeStr)
+	}
+
+	assert.Equal(t, times, timesAgain)
+}
+
+func TestNewWeekdays(t *testing.T) {
+	wd := NewWeekdays(
+		time.Monday,
+		time.Tuesday,
+	)
+
+	var dayStrings []string
+	for _, w := range wd() {
+		dayStrings = append(dayStrings, w.String())
+	}
+
+	var dayStringsAgain []string
+	for _, w := range wd() {
+		dayStringsAgain = append(dayStringsAgain, w.String())
+	}
+
+	assert.Equal(t, dayStrings, dayStringsAgain)
+}
+
+func TestNewDaysOfTheMonth(t *testing.T) {
+	dom := NewDaysOfTheMonth(1, 2, 3)
+
+	var domInts []int
+	for _, d := range dom() {
+		domInts = append(domInts, d)
+	}
+
+	var domIntsAgain []int
+	for _, d := range dom() {
+		domIntsAgain = append(domIntsAgain, d)
+	}
+
+	assert.Equal(t, domInts, domIntsAgain)
+}