func NewFixedTimeSource(t time.Time) *FixedTimeSource {
	return &FixedTimeSource{fakeTime: t}
}
NewFixedTimeSource creates a FixedTimeSource instance
package util
import "time"
type TimeSource interface {
	Now() time.Time
}
type SystemTimeSource struct{}
func (s SystemTimeSource) Now() time.Time {
	return time.Now()
}
type FixedTimeSource struct {
	fakeTime time.Time
}