Fix: SNS Delete subscriptions on topic deletion (#3410)

* Fix:Delete subscriptions on delete topic

* Changed tests

Co-authored-by: usmankb <usman@krazybee.com>

moto/sns/models.py

@@ -426,8 +426,15 @@ class SNSBackend(BaseBackend):
     def list_topics(self, next_token=None):
         return self._get_values_nexttoken(self.topics, next_token)
 
+    def delete_topic_subscriptions(self, topic):
+        for key, value in self.subscriptions.items():
+            if value.topic == topic:
+                self.subscriptions.pop(key)
+
     def delete_topic(self, arn):
         try:
+            topic = self.get_topic(arn)
+            self.delete_topic_subscriptions(topic)
             self.topics.pop(arn)
         except KeyError:
             raise SNSNotFoundError("Topic with arn {0} not found".format(arn))

tests/test_sns/test_subscriptions.py

@@ -72,9 +72,7 @@ def test_deleting_subscriptions_by_deleting_topic():
     subscriptions = conn.get_all_subscriptions()["ListSubscriptionsResponse"][
         "ListSubscriptionsResult"
     ]["Subscriptions"]
-    subscriptions.should.have.length_of(1)
+    subscriptions.should.have.length_of(0)
-    subscription = subscriptions[0]
-    subscription["SubscriptionArn"].should.equal(subscription_arn)
 
     # Now delete hanging subscription
     conn.unsubscribe(subscription_arn)

tests/test_sns/test_subscriptions_boto3.py

@@ -7,7 +7,7 @@ import sure  # noqa
 from botocore.exceptions import ClientError
 from nose.tools import assert_raises
 
-from moto import mock_sns
+from moto import mock_sns, mock_sqs
 from moto.sns.models import (
     DEFAULT_PAGE_SIZE,
     DEFAULT_EFFECTIVE_DELIVERY_POLICY,
@@ -124,11 +124,9 @@ def test_unsubscribe_from_deleted_topic():
     topics = topics_json["Topics"]
     topics.should.have.length_of(0)
 
-    # And the subscription should still be left
+    # as per the documentation deleting a topic deletes all the subscriptions
     subscriptions = client.list_subscriptions()["Subscriptions"]
-    subscriptions.should.have.length_of(1)
+    subscriptions.should.have.length_of(0)
-    subscription = subscriptions[0]
-    subscription["SubscriptionArn"].should.equal(subscription_arn)
 
     # Now delete hanging subscription
     client.unsubscribe(SubscriptionArn=subscription_arn)
@@ -304,6 +302,28 @@ def test_creating_subscription_with_attributes():
         )
 
 
+@mock_sns
+@mock_sqs
+def test_delete_subscriptions_on_delete_topic():
+    sqs = boto3.client("sqs", region_name="us-east-1")
+    conn = boto3.client("sns", region_name="us-east-1")
+
+    queue = sqs.create_queue(QueueName="test-queue")
+    topic = conn.create_topic(Name="some-topic")
+
+    conn.subscribe(
+        TopicArn=topic.get("TopicArn"), Protocol="sqs", Endpoint=queue.get("QueueUrl")
+    )
+    subscriptions = conn.list_subscriptions()["Subscriptions"]
+
+    subscriptions.should.have.length_of(1)
+
+    conn.delete_topic(TopicArn=topic.get("TopicArn"))
+
+    subscriptions = conn.list_subscriptions()["Subscriptions"]
+    subscriptions.should.have.length_of(0)
+
+
 @mock_sns
 def test_set_subscription_attributes():
     conn = boto3.client("sns", region_name="us-east-1")