Increased test coverage for forms.ImageField.to_python().

tests/forms_tests/field_tests/test_imagefield.py

@@ -1,7 +1,9 @@
 import os
 import unittest
 
-from django.core.files.uploadedfile import SimpleUploadedFile
+from django.core.files.uploadedfile import (
+    SimpleUploadedFile, TemporaryUploadedFile,
+)
 from django.forms import (
     ClearableFileInput, FileInput, ImageField, ValidationError, Widget,
 )
@@ -69,6 +71,19 @@ class ImageFieldTest(FormFieldAssertionsMixin, SimpleTestCase):
         with self.assertRaisesMessage(ValidationError, 'File extension “txt” is not allowed.'):
             f.clean(img_file)
 
+    def test_corrupted_image(self):
+        f = ImageField()
+        img_file = SimpleUploadedFile('not_an_image.jpg', b'not an image')
+        msg = (
+            'Upload a valid image. The file you uploaded was either not an '
+            'image or a corrupted image.'
+        )
+        with self.assertRaisesMessage(ValidationError, msg):
+            f.clean(img_file)
+        with TemporaryUploadedFile('not_an_image_tmp.png', 'text/plain', 1, 'utf-8') as tmp_file:
+            with self.assertRaisesMessage(ValidationError, msg):
+                f.clean(tmp_file)
+
     def test_widget_attrs_default_accept(self):
         f = ImageField()
         # Nothing added for non-FileInput widgets.