This is Perl module Sub::Spy.

INSTALLATION

Install cpanm (App::cpanminus) and then run the following command to install
Sub::Spy:

   $ cpanm Sub::Spy

If you get an archive of this distribution, unpack it and build it
as per the usual:

   $ tar xzf Sub-Spy-$version.tar.gz
   $ cd Sub-Spy-$version
   $ perl Makefile.PL
   $ make && make test

Then install it:

   $ make install

DOCUMENTATION

Sub::Spy documentation is available as in POD. So you can do:

   $ perldoc Sub::Spy

to read the documentation online with your favorite pager.

LICENSE AND COPYRIGHT

Copyright (c) 2011, Naosuke Yokoe. All rights reserved.

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.