Use lru_cache for tokenization tests (#36818)

* fix

* fix

* fix

* fix

---------

Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

tests/models/plbart/test_tokenization_plbart.py

@@ -45,12 +45,13 @@ class PLBartTokenizationTest(TokenizerTesterMixin, unittest.TestCase):
     rust_tokenizer_class = None
     test_rust_tokenizer = False
 
-    def setUp(self):
-        super().setUp()
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
 
         # We have a SentencePiece fixture for testing
         tokenizer = PLBartTokenizer(SAMPLE_VOCAB, language_codes="base", keep_accents=True)
-        tokenizer.save_pretrained(self.tmpdirname)
+        tokenizer.save_pretrained(cls.tmpdirname)
 
     def test_full_base_tokenizer(self):
         tokenizer = PLBartTokenizer(SAMPLE_VOCAB, language_codes="base", keep_accents=True)