@Test
  public void testWithXChaCha20Poly1305Key_noPrefix_works() throws Exception {
    Assume.assumeFalse(TinkFips.useOnlyFips());
    Assume.assumeTrue(XChaCha20Poly1305Jce.isSupported());

    byte[] plaintext = Hex.decode("e1");
    byte[] associatedData = Hex.decode("6384f4714ff18c18");
    byte[] keyBytes =
        Hex.decode("697c197c9e0023c8eee42ddf08c12c46718a436561b0c66d998c81879f7cb74c");
    XChaCha20Poly1305Key key =
        XChaCha20Poly1305Key.create(SecretBytes.copyFrom(keyBytes, InsecureSecretKeyAccess.get()));
    Aead aead = XChaCha20Poly1305Jce.create(key);
    byte[] ciphertext = aead.encrypt(plaintext, associatedData);
    assertThat(ciphertext).hasLength(41); // msg (1) + iv(24) + tag(16)

    assertThat(aead.decrypt(ciphertext, associatedData)).isEqualTo(plaintext);

    byte[] fixedCiphertext =
        Hex.decode(
            "cd78f4533c94648feacd5aef0291b00b454ee3dcdb76dcc8b0e5e35f5332f91bdd2d28e59d68a0b141");
    assertThat(aead.decrypt(fixedCiphertext, associatedData)).isEqualTo(plaintext);
  }
Test case taken from Wycheproof (testcase 5)
https://github.com/google/wycheproof/blob/b063b4aedae951c69df014cd25fa6d69ae9e8cb9/testvectors/xchacha20_poly1305_test.json#L69
java_src/src/test/java/com/google/crypto/tink/aead/internal/XChaCha20Poly1305JceTest.java