@Test public void onCompletion_shouldKeepContext_whenNotSampled() {

  Span span = tracing.tracer().nextSpan(TraceContextOrSamplingFlags.NOT_SAMPLED);
  Callback delegate =
    (metadata, exception) -> assertThat(tracing.tracer().currentSpan()).isEqualTo(span);
  Callback tracingCallback = TracingCallback.create(delegate, span, tracing.currentTraceContext());
  tracingCallback.onCompletion(null, null);
}