Check copies blackify (#10775)

* Apply black before checking copies

* Fix for class methods

* Deal with lonely brackets

* Remove debug and add forward changes

* Separate copies and fix test

* Add black as a test dependency

tests/test_utils_check_copies.py

@@ -19,6 +19,8 @@ import sys
 import tempfile
 import unittest
 
+import black
+
 
 git_repo_path = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
 sys.path.append(os.path.join(git_repo_path, "utils"))
@@ -66,6 +68,7 @@ class CopyCheckTester(unittest.TestCase):
         code = comment + f"\nclass {class_name}(nn.Module):\n" + class_code
         if overwrite_result is not None:
             expected = comment + f"\nclass {class_name}(nn.Module):\n" + overwrite_result
+        code = black.format_str(code, mode=black.FileMode([black.TargetVersion.PY35], line_length=119))
         fname = os.path.join(self.transformer_dir, "new_code.py")
         with open(fname, "w") as f:
             f.write(code)
@@ -103,7 +106,7 @@ class CopyCheckTester(unittest.TestCase):
         )
 
         # Copy consistency with a really long name
-        long_class_name = "TestModelWithAReallyLongNameBecauseSomePeopleLikeThatForSomeReasonIReallyDontUnderstand"
+        long_class_name = "TestModelWithAReallyLongNameBecauseSomePeopleLikeThatForSomeReason"
         self.check_copy_consistency(
             f"# Copied from transformers.models.bert.modeling_bert.BertLMPredictionHead with Bert->{long_class_name}",
             f"{long_class_name}LMPredictionHead",