Remove dependency on pytest for running tests (#2055)

* Switch to plain unittest for skipping slow tests.

Add a RUN_SLOW environment variable for running them.

* Switch to plain unittest for PyTorch dependency.

* Switch to plain unittest for TensorFlow dependency.

* Avoid leaking open files in the test suite.

This prevents spurious warnings when running tests.

* Fix unicode warning on Python 2 when running tests.

The warning was:

    UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal

* Support running PyTorch tests on a GPU.

Reverts 27e015bd.

* Tests no longer require pytest.

* Make tests pass on cuda

transformers/tests/modeling_auto_test.py

@@ -18,11 +18,12 @@ from __future__ import print_function
 
 import unittest
 import shutil
-import pytest
 import logging
 
 from transformers import is_torch_available
 
+from .utils import require_torch, slow
+
 if is_torch_available():
     from transformers import (AutoConfig, BertConfig,
                                     AutoModel, BertModel,
@@ -33,12 +34,11 @@ if is_torch_available():
 
     from .modeling_common_test import (CommonTestCases, ids_tensor)
     from .configuration_common_test import ConfigTester
-else:
-    pytestmark = pytest.mark.skip("Require Torch")
 
 
+@require_torch
 class AutoModelTest(unittest.TestCase):
-    @pytest.mark.slow
+    @slow
     def test_model_from_pretrained(self):
         logging.basicConfig(level=logging.INFO)
         for model_name in list(BERT_PRETRAINED_MODEL_ARCHIVE_MAP.keys())[:1]:
@@ -53,7 +53,7 @@ class AutoModelTest(unittest.TestCase):
             for value in loading_info.values():
                 self.assertEqual(len(value), 0)
 
-    @pytest.mark.slow
+    @slow
     def test_lmhead_model_from_pretrained(self):
         logging.basicConfig(level=logging.INFO)
         for model_name in list(BERT_PRETRAINED_MODEL_ARCHIVE_MAP.keys())[:1]:
@@ -66,7 +66,7 @@ class AutoModelTest(unittest.TestCase):
             self.assertIsNotNone(model)
             self.assertIsInstance(model, BertForMaskedLM)
 
-    @pytest.mark.slow
+    @slow
     def test_sequence_classification_model_from_pretrained(self):
         logging.basicConfig(level=logging.INFO)
         for model_name in list(BERT_PRETRAINED_MODEL_ARCHIVE_MAP.keys())[:1]:
@@ -79,7 +79,7 @@ class AutoModelTest(unittest.TestCase):
             self.assertIsNotNone(model)
             self.assertIsInstance(model, BertForSequenceClassification)
 
-    @pytest.mark.slow
+    @slow
     def test_question_answering_model_from_pretrained(self):
         logging.basicConfig(level=logging.INFO)
         for model_name in list(BERT_PRETRAINED_MODEL_ARCHIVE_MAP.keys())[:1]: