message: subscriber: add filter test for recording after creation
  This adds a test that when a field value is recorded after a span is
  created, and the new value changes the filter level for the span, the
  filter updates accordingly.
diff: @@ -74,3 +74,39 @@ fn field_filter_spans() {
  finished.assert_finished();
  }
  +
  +#[test]
  +fn record_after_created() {
  + let filter: Filter = "[{enabled=true}]=debug"
  + .parse()
  + .expect("filter should parse");
  + let (subscriber, finished) = subscriber::mock()
  + .enter(span::mock().named("span"))
  + .exit(span::mock().named("span"))
  + .record(
  + span::mock().named("span"),
  + field::mock("enabled").with_value(&true),
  + )
  + .enter(span::mock().named("span"))
  + .event(event::mock().at_level(Level::DEBUG))
  + .exit(span::mock().named("span"))
  + .done()
  + .run_with_handle();
  + let subscriber = subscriber.with(filter);
  +
  + with_default(subscriber, || {
  + let span = tracing::info_span!("span", enabled = false);
  + span.in_scope(|| {
  + tracing::debug!("i'm disabled!");
  + });
  +
  + span.record("enabled", &true);
  + span.in_scope(|| {
  + tracing::debug!("i'm enabled!");
  + });
  +
  + tracing::debug!("i'm also disabled");
  + });
  +
  + finished.assert_finished();
  +}
  