DynamoDB - DELETE item from nested sets

tests/test_dynamodb2/test_dynamodb_table_with_range_key.py

@@ -1347,7 +1347,7 @@ def test_update_item_add_with_expression():
 
 
 @mock_dynamodb2
-def test_update_item_add_with_nested_sets_and_expression_names():
+def test_update_item_add_with_nested_sets():
     table = _create_table_with_range_key()
 
     item_key = {"forum_name": "the-key", "subject": "123"}
@@ -1383,6 +1383,32 @@ def test_update_item_add_with_nested_sets_and_expression_names():
     dict(table.get_item(Key=item_key)["Item"]).should.equal(current_item)
 
 
+@mock_dynamodb2
+def test_update_item_delete_with_nested_sets():
+    table = _create_table_with_range_key()
+
+    item_key = {"forum_name": "the-key", "subject": "123"}
+    current_item = {
+        "forum_name": "the-key",
+        "subject": "123",
+        "nested": {"str_set": {"item1", "item2", "item3"}},
+    }
+
+    # Put an entry in the DB to play with
+    table.put_item(Item=current_item)
+
+    # Update item to add a string value to a nested string set
+    table.update_item(
+        Key=item_key,
+        UpdateExpression="DELETE nested.str_set :v",
+        ExpressionAttributeValues={":v": {"item3"}},
+    )
+    current_item["nested"]["str_set"] = current_item["nested"]["str_set"].difference(
+        {"item3"}
+    )
+    dict(table.get_item(Key=item_key)["Item"]).should.equal(current_item)
+
+
 @mock_dynamodb2
 def test_update_item_delete_with_expression():
     table = _create_table_with_range_key()