Yes, modules are preferable. Code like:

require 'test.pl';
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shocks me back to the mid 1990s, Perl 4-style, about fifteen years behind the curve. For both modules and your old style require 'test.pl', try dumping the %INC hash. For example:

use strict;
use warnings;
use Data::Dumper;
require 'test.pl';     # old style
use MyTest;            # module (preferred)
print Dumper(\%INC);   # show PATHs of all files loaded via do, use, r
+equire
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See also the core FindBin module.