### Question:
XOauth2Mechanism extends AbstractMechanism { @Override public byte[] getChallengeResponse(byte[] challenge) { if(challenge != null && challenge.length > 0 && additionalFailureInformation == null) { additionalFailureInformation = new String(challenge, StandardCharsets.UTF_8); } return EMPTY; }  @Override int getPriority(); @Override String getName(); @Override byte[] getInitialResponse(); @Override byte[] getChallengeResponse(byte[] challenge); @Override boolean isApplicable(String username, String password, Principal localPrincipal); @Override String getAdditionalFailureInformation();  }### Answer:
@Test public void testGetChallengeResponse() { XOauth2Mechanism mech = new XOauth2Mechanism(); byte[] response = mech.getChallengeResponse(new byte[1]); assertNotNull(response); assertTrue(response.length == 0); }