There is a Perl script in our environment that I now need to maintain. It is full of bad practices, including using (and re-using) global variables throughout the script. Before I start making changes to the script, I was going to try to write some test scripts so I can have a good regression base. To do this, I was going to use a method described on this page.

I was starting by writing tests for a single subroutine. I put this line somewhat near the top of the script I am testing:

return 1 if ( caller() );

That way, in my test script, I can

require 'script_to_test.pl';

and it won't execute the whole script.

The first subroutine I was going to test makes a lot of use of global variables that are set throughout the script. My thought was to try to override these variables in my test script, something like this:

require_ok('script_to_test.pl');
$var_from_other_script = 'Override Value';
ok( sub_from_other_script() );

Unfortunately (for me), the script I am testing has a massive "my" block at the top, where it declares all variables used in the script. This prevents my test script from seeing/changing the variables in the script I'm running tests against.

I've played with Exporter, Test::Mock..., and some other modules, but it looks like if I want to be able to change any variables I am going to have to modify the other script in some fashion.

My goal is to not change the other script, but to get some good tests running so when I do start changing the other script, I can make sure I didn't break anything. The script is about 10,000 lines (3,000 of them in the main block), so I'm afraid that if I start changing things, I will affect other parts of the code, so having a good test suite would help.

Is this possible? Can a calling script modify variables in another script declared with "my"?

And please don't jump in with answers like, "Just re-write the script from scratch", etc. That may be the best solution, but it doesn't answer my question, and we don't have the time/resources for a re-write.