Add unit tests for middleware

**Description**
Currently middleware lacks proper serialization support.

**Proposed solution**
Add configurable serialization with sensible defaults.

**Priority**: Low/Medium

Locate the middleware implementation and any existing unit-test conventions first; the issue does not name specific files or test entry points. Define done as configurable middleware serialization with sensible defaults, covered by unit tests that verify the default and configured behavior.

Written by the indexing model from the issue text.