Is Perl unit-testing only for modules, not programs?

Question

The docs I find around the ’net and the book I have, Perl Testing, either say or suggest that unit-testing for Perl is usually done when creating modules.

Is this true? Is there no way to unit-test actual programs using Test::More and cousins?

Answer 1

Of course you can test scripts using Test::More. It's just harder, because most scripts would need to be run as a separate process from which you capture the output, and then test it against expected output.

This is why modulinos (see chapter 17 in: brian d foy, Mastering Perl, second edition, O'Reilly, 2014) were developed. A modulino is a script that can also be used as a module. This makes it easier to test, as you can load the modulino into your test script and then test its functions like you would a regular module.

The key feature of a modulino is this:

#! /usr/bin/perl
package App::MyName; # put it in a package

run() unless caller; # Run program unless loaded as a module

sub run {
  ... # your program here
}

The function doesn't have to be called run; you could use main if you're a C programmer. You'd also normally have additional subroutines that run calls as needed.

Then your test scripts can use require "path/to/script" to load your modulino and exercise its functions. Since many scripts involve writing output, and it's often easier to print as you go instead of doing print sub_that_returns_big_string(), you may find Test::Output useful.