public void test_single_identifier() {
Book book = new Book();
Identifier identifier = new Identifier(Identifier.Scheme.ISBN, "1234");
book.getMetadata().addIdentifier(identifier);
FixIdentifierBookProcessor fixIdentifierBookProcessor = new FixIdentifierBookProcessor();
Book resultBook = fixIdentifierBookProcessor.processBook(book);
assertEquals(1, resultBook.getMetadata().getIdentifiers().size());
Identifier actualIdentifier = CollectionUtil.first(resultBook.getMetadata().getIdentifiers());
assertEquals(identifier, actualIdentifier);
}