How can I test that a Perl program compiles from my test suite?

Question

I'm building a regression system (not unit testing) for some Perl scripts.

A core component of the system is

  `perl script.pl @params 1>stdoutfile 2>stderrfile`;

However, in the course of actually working on the scripts, they sometimes don't compile(Shock!). But perl itself will execute correctly. However, I don't know how to detect on stderr whether Perl failed to compile (and therefore wrote to stderr), or my script barfed on input (and therefore wrote to stderr).

How do I detect whether a program executed or not, without exhaustively finding Perl error messages and grepping the stderr file?

Answer 1

Take a look at the $? variable.

From perldoc perlvar:

The status returned by the last pipe close, backtick ("``") command, successful call to wait() or waitpid(), or from the system() operator. This is just the 16-bit status word returned by the traditional Unix wait() system call (or else is made up to look like it). Thus, the exit value of the subprocess is really ("$? >> 8"), and "$? & 127" gives which signal, if any, the process died from, and "$? & 128" reports whether there was a core dump.

Answer 2

It sounds like you need IPC::Open3.

Answer 3

It might be easiest to do this in two steps:

system('$^X -c script.pl');
if ($? == 0) {
    # it compiled, now let's see if it runs
    system('$^X script.pl', @params, '1>stdoutfile', '2>stderrfile');
    # check $?
}
else {
    warn "script.pl didn't compile";
}

Note the use of $^X instead of perl. This is more flexible and robust. It ensures that you're running from the same installation instead of whatever interpreter shows up first in your path. The system call will inherit your environment (including PERL5LIB), so spawning a different version of perl could result in hard-to-diagnose compatibility errors.

Answer 4

Scripts are notoriously hard to test. You have to run them and then scrape their output. You can't unit test their guts... or can you?

#!/usr/bin/perl -w

# Only run if we're the file being executed by Perl
main() if $0 eq __FILE__;

sub main {
    ...your code here...
}

1;

Now you can load the script like any other library.

#!/usr/bin/perl -w

use Test::More;

require_ok("./script.pl");

You can even run and test main(). Test::Output is handy for capturing the output. You can say local @ARGV to control arguments or you can change main() to take @ARGV as an argument (recommended).

Then you can start splitting main() up into smaller routines which you can easily unit test.