Add unit tests for validation

**Feature request**
It would be great to have compression for middleware.

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

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

No file, test, or entry point is named. Start by locating middleware configuration and validation code, then determine where the `enable_compression` option belongs and how existing validation tests are organized. Done means the option defaults to `false`, compression behavior is covered by unit tests, and the requested middleware configuration works.

Written by the indexing model from the issue text.