I tend to start my modules in exactly the same way as my scripts:

#! perl -slw
use strict;
package fred;
...
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But that's because I often end my modules with:

return 1 if caller;
package main;
fred->import;

## code that tests the package above goes here.
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In this way, running the module as a perl fred.pm runs the test.

This keeps the tests with the tested code, ensures it is kept up to date with that code and acts as documentation for its use. To my mind, this is a 3 way win.