Fix #6096: MBartTokenizer's mask token (#6098)

tests/test_modeling_mbart.py

@@ -123,6 +123,7 @@ class MBartEnroIntegrationTest(AbstractMBartIntegrationTest):
         self.assertEqual(logits.shape, expected_shape)
 
 
+@require_torch
 class MBartCC25IntegrationTest(AbstractMBartIntegrationTest):
     checkpoint_name = "facebook/mbart-large-cc25"
     src_text = [
@@ -140,3 +141,14 @@ class MBartCC25IntegrationTest(AbstractMBartIntegrationTest):
         )
         decoded = self.tokenizer.batch_decode(translated_tokens, skip_special_tokens=True)
         self.assertEqual(self.tgt_text[0], decoded[0])
+
+    @slow
+    def test_fill_mask(self):
+        inputs = self.tokenizer.prepare_translation_batch(["One of the best <mask> I ever read!"]).to(torch_device)
+        outputs = self.model.generate(
+            inputs["input_ids"], decoder_start_token_id=self.tokenizer.lang_code_to_id["en_XX"], num_beams=1
+        )
+        prediction: str = self.tokenizer.batch_decode(
+            outputs, clean_up_tokenization_spaces=True, skip_special_tokens=True
+        )[0]
+        self.assertEqual(prediction, "of the best books I ever read!")