@Test public void joinSpan_decorates() {

  propagationFactory = baggageFactory;
  TraceContext incoming = TraceContext.newBuilder().traceId(1L).spanId(2L).sampled(true)
    .shared(true).build();
  TraceContext joined = tracer.joinSpan(incoming).context();
  assertThat(joined).isNotSameAs(incoming);
  assertThat(joined.extra()).isNotEmpty();
}