mocktracer/mockspan.go
func (s *MockSpan) String() string {
	return fmt.Sprintf(
		"traceId=%d, spanId=%d, parentId=%d, sampled=%t, name=%s",
		s.SpanContext.TraceID, s.SpanContext.SpanID, s.ParentID,
		s.SpanContext.Sampled, s.OperationName)
}
func (s *MockSpan) String() string {
	return fmt.Sprintf(
		"traceId=%d, spanId=%d, parentId=%d, sampled=%t, name=%s",
		s.SpanContext.TraceID, s.SpanContext.SpanID, s.ParentID,
		s.SpanContext.Sampled, s.OperationName)
}
// String allows printing span for debugging