Ok, after I found the documentation drupal documentation I get it! The naming of the link list must be:

* @ContentEntityType(
*   id = "mytest",
*   links = {
*     "canonical" = "/tested/{mytest}",
*     "delete-form" = "/tested/{mytest}/delete", // EDIT! 
*     "collection" = "/tested"
*   },
* )

That's all!

Ok, after I found the documentation at drupal documentation I get it! The naming of the link list must be:

* @ContentEntityType(
*   id = "mytest",
*   links = {
*     "canonical" = "/tested/{mytest}",
*     "delete-form" = "/tested/{mytest}/delete", // EDIT! 
*     "collection" = "/tested"
*   },
* )

That's all!