mocktracer/mockspan.go
func (s *MockSpan) Tags() map[string]interface{} {
	s.RLock()
	defer s.RUnlock()
	tags := make(map[string]interface{})
	for k, v := range s.tags {
		tags[k] = v
	}
	return tags
}
func (s *MockSpan) Tags() map[string]interface{} {
	s.RLock()
	defer s.RUnlock()
	tags := make(map[string]interface{})
	for k, v := range s.tags {
		tags[k] = v
	}
	return tags
}
// Tags returns a copy of tags accumulated by the span so far