@Test public void tag() {

  span.start();
  try (SpanInScope ws = tracing.tracer().withSpanInScope(span)) {
    spanCustomizer.tag("foo", "bar");
  }
  span.flush();
  assertThat(spans).flatExtracting(s -> s.tags().entrySet())
    .containsExactly(entry("foo", "bar"));
}