mocktracer/mockspan.go
func (s *MockSpan) Tag(k string) interface{} {
	s.RLock()
	defer s.RUnlock()
	return s.tags[k]
}
func (s *MockSpan) Tag(k string) interface{} {
	s.RLock()
	defer s.RUnlock()
	return s.tags[k]
}
func ( s * MockSpan ) Tag ( k string ) interface { } { s . RLock ( ) defer s . RUnlock ( ) return s . tags [ k ] }
// Tag returns a single tag
Tag returns a single tag