In recent years we've seen an explosion of powerful web technologies in Perl not at the least due to the creation of the PSGI specification.

Plack provides the Plack::Middleware class that makes the process of modifying the response easier, and along with Plack::Util helps us deal with the slightly more complex cases where there's a callback for a response from our inner class:

Plack::Test

Another great thing about abstracting away the actual webserver that our PSGI application is talking to is that we don't actually have to have a real webserver at the outer layer at all! If we just want to test our application we can do this in process by just sending input to the anonymous subroutine and examining the return values.