public <T> Span nextSpanWithParent(SamplerFunction<T> samplerFunction, T arg,
    @Nullable TraceContext parent) {
    return _toSpan(parent, nextContext(samplerFunction, arg, parent));
  }
@Test void nextSpanWithParent_overrideToMakeNewTrace() {
    Span span;
    try (Scope scope = currentTraceContext.newScope(context)) {
      span = tracer.nextSpanWithParent(deferDecision(), false, null);
    }

    assertThat(span.context().parentId()).isNull();
  }