Expose get_config() on ModelTesters (#12812)

* Expose get_config() on ModelTesters

* Typo

tests/test_modeling_bert.py

@@ -16,7 +16,7 @@
 
 import unittest
 
-from transformers import is_torch_available
+from transformers import BertConfig, is_torch_available
 from transformers.models.auto import get_values
 from transformers.testing_utils import require_torch, slow, torch_device
 
@@ -30,7 +30,6 @@ if is_torch_available():
 
     from transformers import (
         MODEL_FOR_PRETRAINING_MAPPING,
-        BertConfig,
         BertForMaskedLM,
         BertForMultipleChoice,
         BertForNextSentencePrediction,
@@ -112,7 +111,15 @@ class BertModelTester:
             token_labels = ids_tensor([self.batch_size, self.seq_length], self.num_labels)
             choice_labels = ids_tensor([self.batch_size], self.num_choices)
 
-        config = BertConfig(
+        config = self.get_config()
+
+        return config, input_ids, token_type_ids, input_mask, sequence_labels, token_labels, choice_labels
+
+    def get_config(self):
+        """
+        Returns a tiny configuration by default.
+        """
+        return BertConfig(
             vocab_size=self.vocab_size,
             hidden_size=self.hidden_size,
             num_hidden_layers=self.num_hidden_layers,
@@ -127,8 +134,6 @@ class BertModelTester:
             initializer_range=self.initializer_range,
         )
 
-        return config, input_ids, token_type_ids, input_mask, sequence_labels, token_labels, choice_labels
-
     def prepare_config_and_inputs_for_decoder(self):
         (
             config,