mocktracer/mockspan.go
func (s *MockSpan) Finish() {
	s.Lock()
	s.FinishTime = time.Now()
	s.Unlock()
	s.tracer.recordSpan(s)
}
func (s *MockSpan) Finish() {
	s.Lock()
	s.FinishTime = time.Now()
	s.Unlock()
	s.tracer.recordSpan(s)
}
// Finish belongs to the Span interface