Fixed #27188 -- Allowed using unique=True with FileField.

Thanks Tim Graham for the initial patch.

tests/model_fields/test_filefield.py

@@ -4,6 +4,7 @@ import unittest
 
 from django.core.files import temp
 from django.core.files.uploadedfile import TemporaryUploadedFile
+from django.db.utils import IntegrityError
 from django.test import TestCase, override_settings
 
 from .models import Document
@@ -61,6 +62,15 @@ class FileFieldTests(TestCase):
         Document.objects.create(myfile='something.txt')
         self.assertEqual(Document.objects.defer('myfile')[0].myfile, 'something.txt')
 
+    def test_unique_when_same_filename(self):
+        """
+        A FileField with unique=True shouldn't allow two instances with the
+        same name to be saved.
+        """
+        Document.objects.create(myfile='something.txt')
+        with self.assertRaises(IntegrityError):
+            Document.objects.create(myfile='something.txt')
+
     @unittest.skipIf(sys.platform.startswith('win'), "Windows doesn't support moving open files.")
     # The file's source and destination must be on the same filesystem.
     @override_settings(MEDIA_ROOT=temp.gettempdir())