### Question:
Jnacl implements Encryptor { @Override public byte[] openAfterPrecomputation(final byte[] cipherText, final Nonce nonce, final SharedKey sharedKey) { LOGGER.debug( "Opening message using nonce {} and shared key {}", nonce, sharedKey); final byte[] paddedInput = pad(cipherText, crypto_secretbox_BOXZEROBYTES); final byte[] paddedOutput = new byte[paddedInput.length]; final int jnaclResult = secretBox.cryptoBoxOpenAfternm( paddedOutput, paddedInput, paddedInput.length, nonce.getNonceBytes(), sharedKey.getKeyBytes()); if (jnaclResult == -1) { LOGGER.error("Could not open sealed payload using shared key {}", sharedKey); throw new EncryptorException("jnacl could not open the payload using the shared key"); } LOGGER.debug("Opened sealed payload for shared key {}", sharedKey); LOGGER.debug( "Opened payload using nonce {} and shared key {}", nonce, sharedKey); return extract(paddedOutput, crypto_secretbox_ZEROBYTES); } Jnacl(final SecureRandom secureRandom, final SecretBox secretBox); @Override SharedKey computeSharedKey(final PublicKey publicKey, final PrivateKey privateKey); @Override byte[] seal(
            final byte[] message, final Nonce nonce, final PublicKey publicKey, final PrivateKey privateKey); @Override byte[] open(
            final byte[] cipherText, final Nonce nonce, final PublicKey publicKey, final PrivateKey privateKey); @Override byte[] sealAfterPrecomputation(final byte[] message, final Nonce nonce, final SharedKey sharedKey); @Override byte[] openAfterPrecomputation(final byte[] cipherText, final Nonce nonce, final SharedKey sharedKey); @Override Nonce randomNonce(); @Override KeyPair generateNewKeys(); @Override SharedKey createSingleKey();  }### Answer:
@Test public void openUsingSharedkeyThrowsExceptionOnFailure() { doReturn(-1) .when(this.secretBox) .cryptoBoxOpenAfternm( any(byte[].class), any(byte[].class), anyInt(), any(byte[].class), eq(sharedKey.getKeyBytes())); final Throwable kaclEx = catchThrowable(() -> this.jnacl.openAfterPrecomputation(message, nonce, sharedKey)); assertThat(kaclEx) .isInstanceOf(EncryptorException.class) .hasMessage("jnacl could not open the payload using the shared key"); verify(this.secretBox) .cryptoBoxOpenAfternm( any(byte[].class), any(byte[].class), anyInt(), any(byte[].class), any(byte[].class)); }
@Test public void openUsingSharedKeySodiumReturnsSuccess() { final byte[] data = new byte[100]; doReturn(1) .when(this.secretBox) .cryptoBoxOpenAfternm( any(byte[].class), eq(data), anyInt(), any(byte[].class), eq(sharedKey.getKeyBytes())); final byte[] results = this.jnacl.openAfterPrecomputation(data, nonce, sharedKey); assertThat(results).isNotEmpty(); verify(this.secretBox) .cryptoBoxOpenAfternm( any(byte[].class), any(byte[].class), anyInt(), any(byte[].class), any(byte[].class)); }