I have downloaded JSON.pm from cpan and placed it in Test folder.

While Test::JSON is pure-Perl and doesn't have a lot of dependencies, so it's possible to install it manually, it's usually easier to make the computer do the installation for you. Yes, even you can use CPAN! And cpanm automagically installs modules in your home directory and sets up all environment variables using local::lib, not requiring root priviledges.