Failing test for ResourceWarning on Python 3

Tests/helper.py

@@ -116,13 +116,16 @@ class PillowTestCase(unittest.TestCase):
             result = func()
 
             # Verify some things.
-            self.assertGreaterEqual(len(w), 1)
-            found = False
-            for v in w:
-                if issubclass(v.category, warn_class):
-                    found = True
-                    break
-            self.assertTrue(found)
+            if warn_class is None:
+                self.assertEqual(len(w), 0)
+            else:
+                self.assertGreaterEqual(len(w), 1)
+                found = False
+                for v in w:
+                    if issubclass(v.category, warn_class):
+                        found = True
+                        break
+                self.assertTrue(found)
         return result
 
     def skipKnownBadTest(self, msg=None, platform=None,

Tests/test_image.py

@@ -196,6 +196,16 @@ class TestImage(PillowTestCase):
         im3 = Image.open('Tests/images/effect_spread.png')
         self.assert_image_similar(im2, im3, 110)
 
+    def test_no_resource_warning_on_save(self):
+        # https://github.com/python-pillow/Pillow/issues/835
+        # Arrange
+        test_file = 'Tests/images/hopper.png'
+
+        # Act/Assert
+        with Image.open(test_file) as im:
+            self.assert_warning(None, lambda: im.save('test_img.jpg'))
+
+
 if __name__ == '__main__':
     unittest.main()