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_ctrl_test.py

@@ -16,7 +16,6 @@ from __future__ import division
 from __future__ import print_function
 
 import unittest
-import pytest
 import shutil
 import pdb
 
@@ -25,13 +24,13 @@ from transformers import is_torch_available
 if is_torch_available():
     from transformers import (CTRLConfig, CTRLModel, CTRL_PRETRAINED_MODEL_ARCHIVE_MAP,
                                     CTRLLMHeadModel)
-else:
-    pytestmark = pytest.mark.skip("Require Torch")
 
 from .modeling_common_test import (CommonTestCases, ids_tensor)
 from .configuration_common_test import ConfigTester
+from .utils import require_torch, slow, torch_device
 
 
+@require_torch
 class CTRLModelTest(CommonTestCases.CommonModelTester):
 
     all_model_classes = (CTRLModel, CTRLLMHeadModel) if is_torch_available() else ()
@@ -140,6 +139,7 @@ class CTRLModelTest(CommonTestCases.CommonModelTester):
 
         def create_and_check_ctrl_model(self, config, input_ids, input_mask, head_mask, token_type_ids, *args):
             model = CTRLModel(config=config)
+            model.to(torch_device)
             model.eval()
 
             model(input_ids, token_type_ids=token_type_ids, head_mask=head_mask)
@@ -157,6 +157,7 @@ class CTRLModelTest(CommonTestCases.CommonModelTester):
 
         def create_and_check_lm_head_model(self, config, input_ids, input_mask, head_mask, token_type_ids, *args):
             model = CTRLLMHeadModel(config)
+            model.to(torch_device)
             model.eval()
 
             loss, lm_logits, _ = model(input_ids, token_type_ids=token_type_ids, labels=input_ids)
@@ -202,7 +203,7 @@ class CTRLModelTest(CommonTestCases.CommonModelTester):
         config_and_inputs = self.model_tester.prepare_config_and_inputs()
         self.model_tester.create_and_check_lm_head_model(*config_and_inputs)
 
-    @pytest.mark.slow
+    @slow
     def test_model_from_pretrained(self):
         cache_dir = "/tmp/transformers_test/"
         for model_name in list(CTRL_PRETRAINED_MODEL_ARCHIVE_MAP.keys())[:1]: