@Test public void nextSpan_fromIdContext_resultantSpanIsLocalRoot() {

  TraceIdContext context = TraceIdContext.newBuilder().traceId(1).build();
  Span span = tracer.nextSpan(TraceContextOrSamplingFlags.create(context));
  assertThat(span.context().spanId()).isEqualTo(span.context().localRootId()); // Sanity check
  assertThat(span.context().isLocalRoot()).isTrue();
}