the PSGI manpage is a specification to decouple web server environments
from web application framework code. the Test::WWW::Mechanize manpage is a
subclass of the WWW::Mechanize manpage that incorporates features for web
application testing. The the Test::WWW::Mechanize::PSGI manpage module
meshes the two to allow easy testing of the PSGI manpage applications.

Testing web applications has always been a bit tricky, normally requiring
starting a web server for your application and making real HTTP requests to
it. This module allows you to test the PSGI manpage web applications but
does not require a server or issue HTTP requests. Instead, it passes the
HTTP request object directly to the PSGI manpage. Thus you do not need to
use a real hostname: "http://localhost/" will do. However, this is
optional. The following two lines of code do exactly the same thing:

$mech->get_ok('/action');
$mech->get_ok('http://localhost/action');