def test_number_of_different_books(self):
     Library(self.store, ["Fantasy", "Thriller"])
     self.add_books([self.books[0], self.books[1], self.books[2]], Library)
     self.assertEqual(3, Library.number_of_different_books())
     Library.add_book(self.books[0])
     self.assertEqual(3, Library.number_of_different_books())
     Library.remove_book(self.books[1])
     self.assertEqual(2, Library.number_of_different_books())
     os.remove(os.path.realpath(self.store))