@Test
  public void testWithRfc7539TestVectors() throws Exception {
    for (Rfc7539TestVector test : rfc7539TestVectors) {
      IndCpaCipher cipher = new ChaCha20(test.key, test.initialCounter);
      byte[] out = cipher.decrypt(Bytes.concat(test.nonce, test.ciphertext));
      Truth.assertThat(out).isEqualTo(test.plaintext);
    }
  }
https://tools.ietf.org/html/rfc7539#section-2.4.2
java_src/src/test/java/com/google/crypto/tink/subtle/ChaCha20Test.java