Add unit tests for middleware

**Feature request**
It would be great to have serialization for controllers.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_serialization` with default `false`.

The issue names middleware, controllers, and the enable_serialization configuration option, but no files, tests, or entry points. First locate the middleware and controller configuration paths and existing unit tests, then clarify whether the intended work is adding tests or implementing serialization; done should include the agreed behavior and a default of false.

Written by the indexing model from the issue text.