require_ok() is a function but not a core perl function, $file is a scalar, presumably the name of a file, that is being passed to the function. If you are asking how to "require" a moule in a perl script that is not the way to do it.
but what i need is regarding the automated test ing in Perl. It is the Perl funtion which is inbuilt. you can find in "man perldoc Test::More" (i.e, manual pages of Perl).
It would be great if you can give some information.
Thank you.