@Test void tag_sizeInBytes() {
    TagField field = new TagField(1 << 3 | WIRETYPE_LENGTH_DELIMITED);
    assertThat(field.sizeInBytes(entry("123", "56789")))
      .isEqualTo(0
        + 1 /* tag of embedded key field */ + 1 /* len */ + 3
        + 1 /* tag of embedded value field  */ + 1 /* len */ + 5
        + 1 /* tag of map entry field */ + 1 /* len */
      );
  }
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