### Question:
AbstractSequence { public static boolean identifierEquals(Identifier id1, Identifier id2) { if (null == id1) { return null == id2; } return null != id2 && id1.getValue().equals(id2.getValue()); } protected  AbstractSequence(Identifier i, ProtocolVariation p); Identifier getIdentifier(); ProtocolVariation getProtocol(); String toString(); boolean equals(Object other); int hashCode(); static boolean identifierEquals(Identifier id1, Identifier id2); synchronized boolean isAcknowledged(long m);  }### Answer:
@Test public void testIdentifierEquals() { Identifier id1 = null; Identifier id2 = null; assertTrue(AbstractSequence.identifierEquals(id1, id2)); ObjectFactory factory = new ObjectFactory(); id1 = factory.createIdentifier(); id1.setValue("seq1"); assertFalse(AbstractSequence.identifierEquals(id1, id2)); id2 = factory.createIdentifier(); id2.setValue("seq2"); assertFalse(AbstractSequence.identifierEquals(id1, id2)); id2.setValue("seq1"); assertTrue(AbstractSequence.identifierEquals(id1, id2)); }