mocktracer/mockspan.go
func (s *MockSpan) SetTag(key string, value interface{}) opentracing.Span {
	s.Lock()
	defer s.Unlock()
	if key == string(ext.SamplingPriority) {
		if v, ok := value.(uint16); ok {
			s.SpanContext.Sampled = v > 0
			return s
		}
		if v, ok := value.(int); ok {
			s.SpanContext.Sampled = v > 0
			return s
		}
	}
	s.tags[key] = value
	return s
}
func (s *MockSpan) SetTag(key string, value interface{}) opentracing.Span {
	s.Lock()
	defer s.Unlock()
	if key == string(ext.SamplingPriority) {
		if v, ok := value.(uint16); ok {
			s.SpanContext.Sampled = v > 0
			return s
		}
		if v, ok := value.(int); ok {
			s.SpanContext.Sampled = v > 0
			return s
		}
	}
	s.tags[key] = value
	return s
}
// SetTag belongs to the Span interface