return an error if duration is zero (#701)

errors.go

@@ -9,6 +9,7 @@ var (
 	ErrDailyJobAtTimesNil            = fmt.Errorf("gocron: DailyJob: atTimes must not be nil")
 	ErrDailyJobHours                 = fmt.Errorf("gocron: DailyJob: atTimes hours must be between 0 and 23 inclusive")
 	ErrDailyJobMinutesSeconds        = fmt.Errorf("gocron: DailyJob: atTimes minutes and seconds must be between 0 and 59 inclusive")
+	ErrDurationJobIntervalZero       = fmt.Errorf("gocron: DurationJob: time interval is 0")
 	ErrDurationRandomJobMinMax       = fmt.Errorf("gocron: DurationRandomJob: minimum duration must be less than maximum duration")
 	ErrEventListenerFuncNil          = fmt.Errorf("gocron: eventListenerFunc must not be nil")
 	ErrJobNotFound                   = fmt.Errorf("gocron: job not found")

job.go

@@ -148,6 +148,9 @@ type durationJobDefinition struct {
 }
 
 func (d durationJobDefinition) setup(j *internalJob, _ *time.Location) error {
+	if d.duration == 0 {
+		return ErrDurationJobIntervalZero
+	}
 	j.jobSchedule = &durationJob{duration: d.duration}
 	return nil
 }

scheduler_test.go

@@ -478,6 +478,12 @@ func TestScheduler_NewJobErrors(t *testing.T) {
 			nil,
 			ErrCronJobParse,
 		},
+		{
+			"duration job time interval is zero",
+			DurationJob(0 * time.Second),
+			nil,
+			ErrDurationJobIntervalZero,
+		},
 		{
 			"random with bad min/max",
 			DurationRandomJob(