add tests for (Dataset|Image)Folder (#3477)

* add tests for (Dataset|Image)Folder

* lint

* remove old tests

* cleanup

* more cleanup

* adapt tests

* fix make_dataset

* remove powerset

* readd import

test/test_datasets.py

@@ -57,67 +57,6 @@ class DatasetTestcase(unittest.TestCase):
 
 
 class Tester(DatasetTestcase):
-    def test_imagefolder(self):
-        # TODO: create the fake data on-the-fly
-        FAKEDATA_DIR = get_file_path_2(
-            os.path.dirname(os.path.abspath(__file__)), 'assets', 'fakedata')
-
-        with get_tmp_dir(src=os.path.join(FAKEDATA_DIR, 'imagefolder')) as root:
-            classes = sorted(['a', 'b'])
-            class_a_image_files = [
-                os.path.join(root, 'a', file) for file in ('a1.png', 'a2.png', 'a3.png')
-            ]
-            class_b_image_files = [
-                os.path.join(root, 'b', file) for file in ('b1.png', 'b2.png', 'b3.png', 'b4.png')
-            ]
-            dataset = torchvision.datasets.ImageFolder(root, loader=lambda x: x)
-
-            # test if all classes are present
-            self.assertEqual(classes, sorted(dataset.classes))
-
-            # test if combination of classes and class_to_index functions correctly
-            for cls in classes:
-                self.assertEqual(cls, dataset.classes[dataset.class_to_idx[cls]])
-
-            # test if all images were detected correctly
-            class_a_idx = dataset.class_to_idx['a']
-            class_b_idx = dataset.class_to_idx['b']
-            imgs_a = [(img_file, class_a_idx) for img_file in class_a_image_files]
-            imgs_b = [(img_file, class_b_idx) for img_file in class_b_image_files]
-            imgs = sorted(imgs_a + imgs_b)
-            self.assertEqual(imgs, dataset.imgs)
-
-            # test if the datasets outputs all images correctly
-            outputs = sorted([dataset[i] for i in range(len(dataset))])
-            self.assertEqual(imgs, outputs)
-
-            # redo all tests with specified valid image files
-            dataset = torchvision.datasets.ImageFolder(
-                root, loader=lambda x: x, is_valid_file=lambda x: '3' in x)
-            self.assertEqual(classes, sorted(dataset.classes))
-
-            class_a_idx = dataset.class_to_idx['a']
-            class_b_idx = dataset.class_to_idx['b']
-            imgs_a = [(img_file, class_a_idx) for img_file in class_a_image_files
-                      if '3' in img_file]
-            imgs_b = [(img_file, class_b_idx) for img_file in class_b_image_files
-                      if '3' in img_file]
-            imgs = sorted(imgs_a + imgs_b)
-            self.assertEqual(imgs, dataset.imgs)
-
-            outputs = sorted([dataset[i] for i in range(len(dataset))])
-            self.assertEqual(imgs, outputs)
-
-    def test_imagefolder_empty(self):
-        with get_tmp_dir() as root:
-            with self.assertRaises(FileNotFoundError):
-                torchvision.datasets.ImageFolder(root, loader=lambda x: x)
-
-            with self.assertRaises(FileNotFoundError):
-                torchvision.datasets.ImageFolder(
-                    root, loader=lambda x: x, is_valid_file=lambda x: False
-                )
-
     @mock.patch('torchvision.datasets.SVHN._check_integrity')
     @unittest.skipIf(not HAS_SCIPY, "scipy unavailable")
     def test_svhn(self, mock_check):
@@ -1673,5 +1612,95 @@ class QMNISTTestCase(MNISTTestCase):
             self.assertEqual(len(dataset), info["num_examples"] - 10000)
 
 
+class DatasetFolderTestCase(datasets_utils.ImageDatasetTestCase):
+    DATASET_CLASS = datasets.DatasetFolder
+
+    # The dataset has no fixed return type since it is defined by the loader parameter. For testing, we use a loader
+    # that simply returns the path as type 'str' instead of loading anything. See the 'dataset_args()' method.
+    FEATURE_TYPES = (str, int)
+
+    _IMAGE_EXTENSIONS = ("jpg", "png")
+    _VIDEO_EXTENSIONS = ("avi", "mp4")
+    _EXTENSIONS = (*_IMAGE_EXTENSIONS, *_VIDEO_EXTENSIONS)
+
+    # DatasetFolder has two mutually exclusive parameters: 'extensions' and 'is_valid_file'. One of both is required.
+    # We only iterate over different 'extensions' here and handle the tests for 'is_valid_file' in the
+    # 'test_is_valid_file()' method.
+    DEFAULT_CONFIG = dict(extensions=_EXTENSIONS)
+    ADDITIONAL_CONFIGS = (
+        *datasets_utils.combinations_grid(extensions=[(ext,) for ext in _IMAGE_EXTENSIONS]),
+        dict(extensions=_IMAGE_EXTENSIONS),
+        *datasets_utils.combinations_grid(extensions=[(ext,) for ext in _VIDEO_EXTENSIONS]),
+        dict(extensions=_VIDEO_EXTENSIONS),
+    )
+
+    def dataset_args(self, tmpdir, config):
+        return tmpdir, lambda x: x
+
+    def inject_fake_data(self, tmpdir, config):
+        extensions = config["extensions"] or self._is_valid_file_to_extensions(config["is_valid_file"])
+
+        num_examples_total = 0
+        classes = []
+        for ext, cls in zip(self._EXTENSIONS, string.ascii_letters):
+            if ext not in extensions:
+                continue
+
+            create_example_folder = (
+                datasets_utils.create_image_folder
+                if ext in self._IMAGE_EXTENSIONS
+                else datasets_utils.create_video_folder
+            )
+
+            num_examples = torch.randint(1, 3, size=()).item()
+            create_example_folder(tmpdir, cls, lambda idx: self._file_name_fn(cls, ext, idx), num_examples)
+
+            num_examples_total += num_examples
+            classes.append(cls)
+
+        return dict(num_examples=num_examples_total, classes=classes)
+
+    def _file_name_fn(self, cls, ext, idx):
+        return f"{cls}_{idx}.{ext}"
+
+    def _is_valid_file_to_extensions(self, is_valid_file):
+        return {ext for ext in self._EXTENSIONS if is_valid_file(f"foo.{ext}")}
+
+    @datasets_utils.test_all_configs
+    def test_is_valid_file(self, config):
+        extensions = config.pop("extensions")
+        # We need to explicitly pass extensions=None here or otherwise it would be filled by the value from the
+        # DEFAULT_CONFIG.
+        with self.create_dataset(
+                config, extensions=None, is_valid_file=lambda file: pathlib.Path(file).suffix[1:] in extensions
+        ) as (dataset, info):
+            self.assertEqual(len(dataset), info["num_examples"])
+
+    @datasets_utils.test_all_configs
+    def test_classes(self, config):
+        with self.create_dataset(config) as (dataset, info):
+            self.assertSequenceEqual(dataset.classes, info["classes"])
+
+
+class ImageFolderTestCase(datasets_utils.ImageDatasetTestCase):
+    DATASET_CLASS = datasets.ImageFolder
+
+    def inject_fake_data(self, tmpdir, config):
+        num_examples_total = 0
+        classes = ("a", "b")
+        for cls in classes:
+            num_examples = torch.randint(1, 3, size=()).item()
+            num_examples_total += num_examples
+
+            datasets_utils.create_image_folder(tmpdir, cls, lambda idx: f"{cls}_{idx}.png", num_examples)
+
+        return dict(num_examples=num_examples_total, classes=classes)
+
+    @datasets_utils.test_all_configs
+    def test_classes(self, config):
+        with self.create_dataset(config) as (dataset, info):
+            self.assertSequenceEqual(dataset.classes, info["classes"])
+
+
 if __name__ == "__main__":
     unittest.main()

torchvision/datasets/folder.py

@@ -129,7 +129,7 @@ def make_dataset(
                     if target_class not in available_classes:
                         available_classes.add(target_class)
 
-    empty_classes = available_classes - set(class_to_idx.keys())
+    empty_classes = set(class_to_idx.keys()) - available_classes
     if empty_classes:
         msg = f"Found no valid file for the classes {', '.join(sorted(empty_classes))}. "
         if extensions is not None: