Fixes controller pattern matching, add test coverage

:information_desk_person: The existing pattern matching for controllers misses `application_controller.rb`. 

```ruby
      add_mapping(%r{\Aapp/controllers/(.*)\.rb\z}) { |_, m|
        if m[1] == 'application'
```

These changes update the relevant regular expressions to match those used elsewhere (i.e. L61-2). 

I've also added tests for the remaining pattern matching methods. :lipstick: 

[edit: added further detail around the original problem]
I've updated the doc string to be closer to what is under test.