add tests for Omniglot dataset (#3461)

Co-authored-by: Vasilis Vryniotis <datumbox@users.noreply.github.com>

test/test_datasets.py

@@ -1092,5 +1092,35 @@ class HMDB51TestCase(datasets_utils.VideoDatasetTestCase):
         return num_train_videos if train else (num_videos - num_train_videos)
 
 
+class OmniglotTestCase(datasets_utils.ImageDatasetTestCase):
+    DATASET_CLASS = datasets.Omniglot
+
+    CONFIGS = datasets_utils.combinations_grid(background=(True, False))
+
+    def inject_fake_data(self, tmpdir, config):
+        target_folder = (
+            pathlib.Path(tmpdir) / "omniglot-py" / f"images_{'background' if config['background'] else 'evaluation'}"
+        )
+        os.makedirs(target_folder)
+
+        num_images = 0
+        for name in ("Alphabet_of_the_Magi", "Tifinagh"):
+            num_images += self._create_alphabet_folder(target_folder, name)
+
+        return num_images
+
+    def _create_alphabet_folder(self, root, name):
+        num_images_total = 0
+        for idx in range(torch.randint(1, 4, size=()).item()):
+            num_images = torch.randint(1, 4, size=()).item()
+            num_images_total += num_images
+
+            datasets_utils.create_image_folder(
+                root / name, f"character{idx:02d}", lambda image_idx: f"{image_idx:02d}.png", num_images
+            )
+
+        return num_images_total
+
+
 if __name__ == "__main__":
     unittest.main()