Add test for CIFAR10(0) (#1010)

* added test for CIFAR10(0)

* create CIFAR data on-the-fly

* flake8

* fixed typo

* removed falsely added import

test/test_datasets.py

 import os
+import sys
 import shutil
 import contextlib
 import tempfile
 import unittest
 import mock
+import numpy as np
 import PIL
 import torch
 import torchvision
 
+PYTHON2 = sys.version_info[0] == 2
+if PYTHON2:
+    import cPickle as pickle
+else:
+    import pickle
+
 FAKEDATA_DIR = os.path.join(os.path.dirname(os.path.abspath(__file__)),
                             'assets', 'fakedata')
 
@@ -59,8 +67,62 @@ def get_mnist_data(num_images, cls_name, **kwargs):
         shutil.rmtree(tmp_dir)
 
 
-class Tester(unittest.TestCase):
+@contextlib.contextmanager
+def cifar_root(version):
+    def _get_version_params(version):
+        if version == 'CIFAR10':
+            return {
+                'base_folder': 'cifar-10-batches-py',
+                'train_files': ['data_batch_{}'.format(batch) for batch in range(1, 6)],
+                'test_file': 'test_batch',
+                'target_key': 'labels',
+                'meta_file': 'batches.meta',
+                'classes_key': 'label_names',
+            }
+        elif version == 'CIFAR100':
+            return {
+                'base_folder': 'cifar-100-python',
+                'train_files': ['train'],
+                'test_file': 'test',
+                'target_key': 'fine_labels',
+                'meta_file': 'meta',
+                'classes_key': 'fine_label_names',
+            }
+        else:
+            raise ValueError
+
+    def _make_pickled_file(obj, file):
+        with open(file, 'wb') as fh:
+            pickle.dump(obj, fh, 2)
+
+    def _make_data_file(file, target_key):
+        obj = {
+            'data': np.zeros((1, 32 * 32 * 3), dtype=np.uint8),
+            target_key: [0]
+        }
+        _make_pickled_file(obj, file)
+
+    def _make_meta_file(file, classes_key):
+        obj = {
+            classes_key: ['fakedata'],
+        }
+        _make_pickled_file(obj, file)
+
+    params = _get_version_params(version)
+    with tmp_dir() as root:
+        base_folder = os.path.join(root, params['base_folder'])
+        os.mkdir(base_folder)
 
+        for file in list(params['train_files']) + [params['test_file']]:
+            _make_data_file(os.path.join(base_folder, file), params['target_key'])
+
+        _make_meta_file(os.path.join(base_folder, params['meta_file']),
+                        params['classes_key'])
+
+        yield root
+
+
+class Tester(unittest.TestCase):
     def test_imagefolder(self):
         with tmp_dir(src=os.path.join(FAKEDATA_DIR, 'imagefolder')) as root:
             classes = sorted(['a', 'b'])
@@ -153,6 +215,46 @@ class Tester(unittest.TestCase):
             self.assertTrue(isinstance(target, int))
             self.assertEqual(dataset.class_to_idx['Tinca tinca'], target)
 
+    @mock.patch('torchvision.datasets.cifar.check_integrity')
+    @mock.patch('torchvision.datasets.cifar.CIFAR10._check_integrity')
+    def test_cifar10(self, mock_ext_check, mock_int_check):
+        mock_ext_check.return_value = True
+        mock_int_check.return_value = True
+        with cifar_root('CIFAR10') as root:
+            dataset = torchvision.datasets.CIFAR10(root, train=True, download=True)
+            self.assertEqual(len(dataset), 5)
+            img, target = dataset[0]
+            self.assertTrue(isinstance(img, PIL.Image.Image))
+            self.assertTrue(isinstance(target, int))
+            self.assertEqual(dataset.class_to_idx['fakedata'], target)
+
+            dataset = torchvision.datasets.CIFAR10(root, train=False, download=True)
+            self.assertEqual(len(dataset), 1)
+            img, target = dataset[0]
+            self.assertTrue(isinstance(img, PIL.Image.Image))
+            self.assertTrue(isinstance(target, int))
+            self.assertEqual(dataset.class_to_idx['fakedata'], target)
+
+    @mock.patch('torchvision.datasets.cifar.check_integrity')
+    @mock.patch('torchvision.datasets.cifar.CIFAR10._check_integrity')
+    def test_cifar100(self, mock_ext_check, mock_int_check):
+        mock_ext_check.return_value = True
+        mock_int_check.return_value = True
+        with cifar_root('CIFAR100') as root:
+            dataset = torchvision.datasets.CIFAR100(root, train=True, download=True)
+            self.assertEqual(len(dataset), 1)
+            img, target = dataset[0]
+            self.assertTrue(isinstance(img, PIL.Image.Image))
+            self.assertTrue(isinstance(target, int))
+            self.assertEqual(dataset.class_to_idx['fakedata'], target)
+
+            dataset = torchvision.datasets.CIFAR100(root, train=False, download=True)
+            self.assertEqual(len(dataset), 1)
+            img, target = dataset[0]
+            self.assertTrue(isinstance(img, PIL.Image.Image))
+            self.assertTrue(isinstance(target, int))
+            self.assertEqual(dataset.class_to_idx['fakedata'], target)
+
 
 if __name__ == '__main__':
     unittest.main()