Add TorchHub tests to torchvision (#1319)

* Add Hub tests in torchvision

* Run test_hub in its own interpreter

.travis.yml

@@ -76,6 +76,7 @@ install:
 
 script:
   - pytest --cov-config .coveragerc --cov torchvision --cov $TV_INSTALL_PATH test
+  - pytest test/test_hub.py
 
 after_success:
   # Necessary to run coverage combine to rewrite paths from

test/test_hub.py

+import torch.hub as hub
+import tempfile
+import shutil
+import os
+import sys
+import unittest
+
+
+def sum_of_model_parameters(model):
+    s = 0
+    for p in model.parameters():
+        s += p.sum()
+    return s
+
+
+SUM_OF_PRETRAINED_RESNET18_PARAMS = -12703.99609375
+
+
+@unittest.skipIf('torchvision' in sys.modules,
+                 'TestHub must start without torchvision imported')
+class TestHub(unittest.TestCase):
+    # Only run this check ONCE before all tests start.
+    # - If torchvision is imported before all tests start, e.g. we might find _C.so
+    #   which doesn't exist in downloaded zip but in the installed wheel.
+    # - After the first test is run, torchvision is already in sys.modules due to
+    #   Python cache as we run all hub tests in the same python process.
+
+    def test_load_from_github(self):
+        hub_model = hub.load(
+            'pytorch/vision',
+            'resnet18',
+            pretrained=True,
+            progress=False)
+        self.assertEqual(sum_of_model_parameters(hub_model).item(),
+                         SUM_OF_PRETRAINED_RESNET18_PARAMS)
+
+    def test_set_dir(self):
+        temp_dir = tempfile.gettempdir()
+        hub.set_dir(temp_dir)
+        hub_model = hub.load(
+            'pytorch/vision',
+            'resnet18',
+            pretrained=True,
+            progress=False)
+        self.assertEqual(sum_of_model_parameters(hub_model).item(),
+                         SUM_OF_PRETRAINED_RESNET18_PARAMS)
+        assert os.path.exists(temp_dir + '/pytorch_vision_master')
+        shutil.rmtree(temp_dir + '/pytorch_vision_master')
+
+    def test_list_entrypoints(self):
+        entry_lists = hub.list('pytorch/vision', force_reload=True)
+        self.assertIn('resnet18', entry_lists)
+
+
+if __name__ == "__main__":
+    unittest.main()