Add unit tests for middleware

**Feature request**
It would be great to have caching for parsers.

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

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

Start by reconciling the title's request for middleware unit tests with the body’s parser-caching feature request. Locate the middleware, parser, and configuration entry points, then inspect existing tests and configuration defaults. Done means the intended caching behavior and the `enable_caching` default are covered by tests, but the issue does not identify specific files or test commands.

Written by the indexing model from the issue text.