[Tests] Add Common Test for Training + Fix a couple of bugs (#8415)

* add training tests

* correct longformer

* fix docs

* fix some tests

* fix some more train tests

* remove ipdb

* fix multiple edge case model training

* fix funnel and prophetnet

* clean gpt models

* undo renaming of albert

tests/test_modeling_lxmert.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 
+import copy
 import unittest
 
 from transformers import is_torch_available
@@ -26,7 +27,14 @@ from .test_modeling_common import ModelTesterMixin, ids_tensor
 if is_torch_available():
     import torch
 
-    from transformers import LxmertConfig, LxmertForPreTraining, LxmertForQuestionAnswering, LxmertModel
+    from transformers import (
+        MODEL_FOR_PRETRAINING_MAPPING,
+        MODEL_FOR_QUESTION_ANSWERING_MAPPING,
+        LxmertConfig,
+        LxmertForPreTraining,
+        LxmertForQuestionAnswering,
+        LxmertModel,
+    )
     from transformers.modeling_lxmert import LXMERT_PRETRAINED_MODEL_ARCHIVE_LIST
 
 
@@ -533,6 +541,22 @@ class LxmertModelTest(ModelTesterMixin, unittest.TestCase):
     test_pruning = False
     test_torchscript = False
 
+    # overwrite function because qa models takes different input label shape
+    def _prepare_for_class(self, inputs_dict, model_class, return_labels=False):
+        inputs_dict = copy.deepcopy(inputs_dict)
+
+        if return_labels:
+            if model_class in MODEL_FOR_QUESTION_ANSWERING_MAPPING.values():
+                inputs_dict["labels"] = torch.zeros(
+                    self.model_tester.batch_size, dtype=torch.long, device=torch_device
+                )
+            elif model_class in MODEL_FOR_PRETRAINING_MAPPING.values():
+                # special case for models like BERT that use multi-loss training for PreTraining
+                inputs_dict["labels"] = torch.zeros(
+                    (self.model_tester.batch_size, self.model_tester.seq_length), dtype=torch.long, device=torch_device
+                )
+        return inputs_dict
+
     def setUp(self):
         self.model_tester = LxmertModelTester(self)
         self.config_tester = ConfigTester(self, config_class=LxmertConfig, hidden_size=37)