tests/migrations: test getting a migration that does not exist

Author: bashtanov

tests/rptest/tests/data_migrations_api_test.py

@@ -244,6 +244,15 @@ def assure_not_migratable(self, topic: TopicSpec):
         except requests.exceptions.HTTPError as e:
             pass
 
+    @cluster(num_nodes=3, log_allow_list=MIGRATION_LOG_ALLOW_LIST)
+    def test_listing_inexistent_migration(self):
+        try:
+            self.get_migration(42)
+        except Exception as e:
+            # check 404
+            self.logger.info("f{e}")
+            raise
+
     @cluster(num_nodes=3, log_allow_list=MIGRATION_LOG_ALLOW_LIST)
     def test_creating_with_topic_no_remote_writes(self):
         self.redpanda.set_cluster_config(