Override controller test scaffold for rails 5

I tried to override the controller test generator for scaffolding in rails 5. I found the original file, but can't place it in the template directory.

If I read correctly this post Changing scaffold-controller-generator-templates in Rails, the path should be :

lib/templates/rails/test_unit/controller.rb 

or

lib/templates/rails/test_unit/functional_test.rb # from the scaffold sources

Finally I tested lots of combinaisons of directories and files names, but none work.

Does anybody know how to do that ?