@Test
  public void hChaCha20_testVector() {
    byte[] key = Hex.decode("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f");
    byte[] nonce = Hex.decode("000000090000004a0000000031415927");
    byte[] expected =
        Hex.decode("82413b4227b27bfed30e42508a877d73a0f9e4d58a74a853c12ec41326d3ecdc");
    assertThat(ChaCha20Util.hChaCha20(key, nonce)).isEqualTo(expected);
  }
https://datatracker.ietf.org/doc/html/rfc7539#section-2.3.2
java_src/src/test/java/com/google/crypto/tink/aead/internal/ChaCha20UtilTest.java