[TokenizationRoformerFast] Fix the save and loading (#28527)

* cleanup

* add a test

* update the test

* style

* revert part that allows to pickle the tokenizer

tests/models/roformer/test_tokenization_roformer.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import tempfile
 import unittest
 
 from transformers import RoFormerTokenizer, RoFormerTokenizerFast
@@ -71,6 +72,12 @@ class RoFormerTokenizationTest(TokenizerTesterMixin, unittest.TestCase):
     def test_training_new_tokenizer_with_special_tokens_change(self):
         pass
 
-    # can't serialise custom PreTokenizer
     def test_save_slow_from_fast_and_reload_fast(self):
-        pass
+        for cls in [RoFormerTokenizer, RoFormerTokenizerFast]:
+            original = cls.from_pretrained("alchemab/antiberta2")
+            self.assertEqual(original.encode("生活的真谛是"), [1, 4, 4, 4, 4, 4, 4, 2])
+
+            with tempfile.TemporaryDirectory() as tmp_dir:
+                original.save_pretrained(tmp_dir)
+                new = cls.from_pretrained(tmp_dir)
+            self.assertEqual(new.encode("生活的真谛是"), [1, 4, 4, 4, 4, 4, 4, 2])