@Test void span_write_shared() {
    SPAN.write(buf, CLIENT_SPAN.toBuilder().kind(Span.Kind.SERVER).shared(true).build());

    assertThat(bytes)
      .contains(0b01101000, atIndex(buf.pos() - 2)) // (field_number << 3) | wire_type = 13 << 3 | 0
      .contains(1, atIndex(buf.pos() - 1)); // true
  }
A map entry is an embedded messages: one for field the key and one for the value
zipkin/src/test/java/zipkin2/internal/Proto3ZipkinFieldsTest.java