-- t.pm --
package t;

use t2;

sub testing { print "Testing from t.pm\n"; }

1;

-- t2.pm --
package t2;

require Exporter;
our @ISA = qw(Exporter);
our @EXPORT = qw(testing2);
  
sub testing2 { print "Testing from t2.pm\n"; }

1;

-- test.pl --
#!/usr/bin/perl
use t;

t::testing();
t::testing2();