Doing this with inheritance means you have to redefine run(), because you can't
have multiple is_applicable functions. And then would come the
inconsistency...in some cases it's enough to reimplement is_applicable, but in
other cases not. You can of course create another level of inheritance (as the
original Ruby checks do) to solve this problem

Decorators have a different problem and that is manual tests which still have
is_applicable. Since we got rid of it, it has to instead be changed to
automatic check which returns not_applicable when appropriate. Example:

Original:
class CheckLocale(GenericCheckBase):
    def __init__(self, base):
        ...
        self.automatic = False

    def is_applicable(self):
        return self.has_files('/usr/share/locale/*/LC_MESSAGES/*.mo')

New:
class CheckLocale(GenericCheckBase):
    def __init__(self, base):
        ..,
        self.automatic = True

    def run(self):
        if self.has_files('/usr/share/locale/*/LC_MESSAGES/*.mo'):
            self.set_passed('inconclusive')
        else:
            self.set_passed('not_applicable')