Add regression test for #26

Author: codingjoe

tests/test_tasks.py

@@ -0,0 +1,18 @@
+from unittest.mock import Mock
+
+import pytest
+
+from pictures import tasks
+from tests.testapp.models import SimpleModel
+
+
+@pytest.mark.django_db
+def test_process_picture__file_cannot_be_reopened(image_upload_file):
+    # regression https://github.com/codingjoe/django-pictures/issues/26
+    obj = SimpleModel.objects.create(picture=image_upload_file)
+    setattr(
+        obj.picture.file,
+        "open",
+        Mock(side_effect=ValueError("The file cannot be reopened.")),
+    )
+    tasks._process_picture(obj.picture)