Stubbing/mocking a service in a Dancer2 application - unit-testing

Question

Usually, I have a setup similar to this:
#!/usr/bin/env perl
package Demo;
use Dancer2;
use Moose;
sub get($self, $params) {
my $whatever = ...; # connect with db and do stuff
return $whatever;
}
my $service = Demo->new();
sub make_web_friendly($param) { # no $self, here!
return "Hello $param!";
}
get '/' => sub {
my $response = $service->get(query_parameters);
return make_web_friendly($response);
};
start;
This way, I can separate concerns pretty well and my services are testable without going over a bogus web request via Plack::Test;
However, whenever I test the request, I always also test the service, with goes against this separation.
I would want to provide the Plack Test with a stubbed service that would mock a service answer. So (I assume) either I can make the get action somehow $self-aware, or would have to pass the mocked service to Plack.
# this is put together to showcase the principle, it does not work
package Stub {
use Moose;
use Test::More;
use Data::Dumper;
sub get($self, $params) {
diag "I received:" . Dumper($params);
return "Bianca!";
}
}
my $app = Demo->to_app;
my $test = Plack::Test->create($app);
my $stub = Stub->new();
$test->service($stub);
my $request = HTTP::Request->new( GET => '/' );
my $response = $test->request($request);
is $response, 'Hello, Bianca', 'Bianca was here';
How can I achieve (something like) this?