• You pretend there's an is-a relationship where there isn't one.
• That won't work if two modules include each other.

Newer versions of Exporter recognize the first point and allow you to do

package MyTest;

use strict;
use warnings;

BEGIN {
   our @EXPORT_OK = qw( testroutine );
}

use Exporter qw( import );

# Rest of the code here
...
[download]

The BEGIN is there to address the second point.