It's quite straight forward to check if a request url exists in a store scope via url_rewrites.
However, I'm wondering if there is a way to check if a custom route exists (as they don't have an entry in url_rewrites).
I.e. if I have
<?php class \MyCompany\MyModule\Controller\Index\All extends \Magento\Framework\App\Action\Action
and declared my frontend route
<route id="mymodule" frontName="mymodule">
How to check if mymodule/index/all is a valid request_path (obviously we can try to request this path and will get a HTTP 200 response but I'm trying to avoid going down that path).