Refs #27777 -- Improved docs/added test for File context manager change.

tests/model_fields/test_filefield.py

@@ -3,6 +3,7 @@ import sys
 import unittest
 
 from django.core.files import temp
+from django.core.files.base import ContentFile
 from django.core.files.uploadedfile import TemporaryUploadedFile
 from django.db.utils import IntegrityError
 from django.test import TestCase, override_settings
@@ -83,3 +84,13 @@ class FileFieldTests(TestCase):
             tmp_file_path = tmp_file.temporary_file_path()
             Document.objects.create(myfile=tmp_file)
             self.assertFalse(os.path.exists(tmp_file_path), 'Temporary file still exists')
+
+    def test_open_returns_self(self):
+        """
+        FieldField.open() returns self so it can be used as a context manager.
+        """
+        d = Document.objects.create(myfile='something.txt')
+        # Replace the FileField's file with an in-memory ContentFile, so that
+        # open() doesn't write to disk.
+        d.myfile.file = ContentFile(b'', name='bla')
+        self.assertEqual(d.myfile, d.myfile.open())