@Test void writeList_multiple() {
    byte[] bytes = writer.writeList(List.of(CLIENT_SPAN, CLIENT_SPAN));

    assertThat(bytes)
      .hasSize(writer.sizeInBytes(CLIENT_SPAN) * 2)
      .startsWith((byte) 10, SPAN.sizeOfValue(CLIENT_SPAN));
  }
proto messages always need a key, so the non-list form is just a single-field
zipkin/src/test/java/zipkin2/internal/Proto3SpanWriterTest.java