public Span handleReceive(RpcServerRequest request) {
    Span span = nextSpan(extractor.extract(request), request);
    return handleStart(request, span);
  }
@Test void handleReceive_samplerSeesRpcServerRequest() {
    SamplerFunction<RpcRequest> serverSampler = mock(SamplerFunction.class);
    init(httpTracingBuilder(tracingBuilder()).serverSampler(serverSampler));

    handler.handleReceive(request);

    verify(serverSampler).trySample(request);
  }