The conn you get from MyApp.ConnTest is not linked to any particular endpoint. You could have multiples of those in your project. Therefore you need to link that conn (basically a plain request) to an endpoint before you can use it to unit test things depending on a conn for a specific endpoint. Without that linkage the url generation doesn’t know which host to use, which path was requested, if the endpoint was mounted to a subfolder, …
For most ConnTests those things are set when you do get conn, path, …. but for unit tests you need to handle it on your own.
