Updated tests for entities and controllers + adding tests for accessibility

Updated tests for controllers and entities. Adding accessibility tests for pages.

Notes: the accessibility tests require/use node.js, npm, and the [nature/pa11y](https://github.com/nature/pa11y) library.

Task list:

- [x] Add accessibility tests for home routes
- [x] Add accessibility tests for auth routes
- [ ] Add accessibility tests for users (`/users/:id/:action`) routes