mocktracer/mockspan.go
func (s *MockSpan) Context() opentracing.SpanContext {
	s.Lock()
	defer s.Unlock()
	return s.SpanContext
}
func (s *MockSpan) Context() opentracing.SpanContext {
	s.Lock()
	defer s.Unlock()
	return s.SpanContext
}
// Context belongs to the Span interface