### Question:
PlainMechanism extends AbstractMechanism { @Override public byte[] getChallengeResponse(byte[] challenge) { 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);  }### Answer:
@Test public void testGetChallengeResponse() { PlainMechanism mech = new PlainMechanism(); byte[] response = mech.getChallengeResponse(new byte[1]); assertNotNull(response); assertTrue(response.length == 0); }