You can do something like this:

sub main 
{
  until (should_stop())
  {
    # code goes here
  }
}

main unless caller;
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Suppose we are running the script from crontab, will that be considered as a caller?

caller only knows about callers in the same perl process. So do or require will not trigger a main call, while cron, or even system "perl script.pl"; will.

I guess you're looking for something called a Modulino, e.g.: http://www.drdobbs.com/scripts-as-modules/184416165

The basic idea is to make your script behave as a program when executing and to behave as a package while testing.

Maybe define/override the function should_stop so it always returns false?

I like that. So I should put something like this in my test.pl?

local *should_stop = sub { return 1; }; 

require ('wrong_settings_detection.pl');
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Also,suppose i change my code to:

package X;
sub func1 {....}
sub func2 {....}
until (should_stop()){...}
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Can i export the package into my test.pl ???

You can still override the things:

package X;
use strict;
use Exporter 'import';
use vars '@EXPORT_OK';
@EXPORT_OK = qw(func1 func2 );
sub func1 { ... };
sub func2 { ... };

sub should_stop { ... };

until (should_stop()){...}
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And then in your test file:

local *X::should_stop = sub { return 1 };
require X;
X->import('func1');
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But that is precisely what you should do.