ok: add_attrs
ok: add_attrs'
ok: add_event
ok: add_event'
ok: add_links
ok: add_links'
ok: set_status
ok: set_kind
ok: record_exception
span dummy at the end: { trace_id = <bytes len=16>;
                         span_id = <bytes len=8>;
                         trace_state = "" (* absent *);
                         parent_span_id = <bytes len=0> (* absent *);
                         flags = 0 (* absent *);
                         name = "" (* absent *);
                         kind = Span_kind_unspecified (* absent *);
                         start_time_unix_nano = 0 (* absent *);
                         end_time_unix_nano = 0 (* absent *);
                         attributes = [];
                         dropped_attributes_count = 0 (* absent *);
                         events = [];
                         dropped_events_count = 0 (* absent *);
                         links = [];
                         dropped_links_count = 0 (* absent *);
                         status = None;
                       }
all ok