Collector { String idString(Span span) { return span.traceId() + "/" + span.id(); } Collector(Builder builder); static Builder newBuilder(Class<?> loggingClass); void accept(List<Span> spans, Callback<Void> callback); void accept(List<Span> spans, Callback<Void> callback, Executor executor); void acceptSpans(ByteBuffer encoded, SpanBytesDecoder decoder, Callback<Void> callback,
    Executor executor); void acceptSpans(byte[] serialized, Callback<Void> callback); void acceptSpans(
    byte[] serializedSpans, BytesDecoder<Span> decoder, Callback<Void> callback);  }
@Test public void storeSpansCallback_toStringIncludesSpanIds() { Span span2 = CLIENT_SPAN.toBuilder().id("3").build(); when(collector.idString(span2)).thenReturn("3"); assertThat(collector.new StoreSpans(asList(CLIENT_SPAN, span2))) .hasToString("StoreSpans([1, 3])"); }