Trouble moving block elements from core to application

First time working with 5.7, I worked with 5.6 about a year ago.

I'm trying make changes to the default form block. Specifically, the mini_survey.php file

When I move that file from the core folder to the application folder (~/application/blocks/form) it isn't working. Do I have to edit anything in any file in order to make this work?

On a related note, I tried moving the controller.php file from core to application and got the following error: Class '\Application\Block\Form\Controller' not found

Do I have to edit the namespace or any other part of the controller when I move it? I know in 5.6, I could just copy the file out of core and work without immediately. Are there more steps involved with 5.7?

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WillemAnchor replied on at Permalink Reply
for example a content block's controller should now start like:
namespace Application\Block\Content;
class Controller extends \Concrete\Block\Content\Controller

You can also find more info in the docs