Neither File::Lib nor Lib::File (and you use both names so it's impossible to know which one you really mean) are on the CPAN so it's hard to be much help as we can't see the code of the module in question. Where did this module come from?

An export tag like :filetest is usually created using the Exporter module and the @EXPORT_TAGS variable. You might like to look at the documentation for Exporter to see how it's supposed to work and then compare that with how your module works.

I could not find the module on CPAN, but google found this:
http://www.lackas.net/imp/docs/Lib/File.html

Unfortunately I don't see the code listed, so I cannot check what the module exports. You can though. Find this file (Lib/File.pm) and look through the source to see whether it uses the Exporter module to control what tokens it exports. If so, look for %EXPORT_TAGS.

You should also search for 'sub import', which would be custom import behaviour.

Perhaps you meant to do this: use filetest;
The filetest module is listed as "Perl pragma to control the filetest permission operators".
Read perldoc filetest for more information.

Edit: davorg - made link clickable