Fixed item last_modified to update on term delete

django/website/data_layer/models.py

@@ -55,7 +55,7 @@ Item = Message
 @receiver(models.signals.m2m_changed, sender=Item.terms.through,
           dispatch_uid="data_layer.models.terms_signal_handler")
 def terms_signal_handler(sender, **kwargs):
-    if kwargs.get('action') != 'post_add':
+    if kwargs.get('action') not in ('post_add', 'post_remove'):
         return
 
     if kwargs.get('reverse'):

django/website/data_layer/tests/item_tests.py

@@ -66,6 +66,18 @@ def test_last_modified_date_updates_on_item_category_add(
         assert num_updates(orig_last_modified, last_modified(item)) == 1
 
 
+@pytest.mark.django_db
+def test_last_modified_date_updates_on_item_category_delete(
+        item, mock_time_now):
+    with patch('django.utils.timezone.now', new=mock_time_now):
+        term = TermFactory()
+        item.terms.add(term)
+        orig_last_modified = last_modified(item)
+        item.terms.remove(term)
+
+        assert num_updates(orig_last_modified, last_modified(item)) == 1
+
+
 @pytest.mark.django_db
 def test_last_modified_date_updates_on_category_item_add(
         item, mock_time_now):