@Test void emoji() {
    byte[] emojiBytes = {(byte) 0xF0, (byte) 0x9F, (byte) 0x98, (byte) 0x81};
    String emoji = new String(emojiBytes, UTF_8);
    assertThat(WriteBuffer.utf8SizeInBytes(emoji))
      .isEqualTo(emojiBytes.length);

    byte[] bytes = new byte[emojiBytes.length];
    WriteBuffer.wrap(bytes).writeUtf8(emoji);
    assertThat(bytes)
      .isEqualTo(emojiBytes);
  }
Uses test data and codepoint wrapping trick from okhttp3.FormBodyTest
zipkin/src/test/java/zipkin2/internal/WriteBufferTest.java