I am revising a Perl program and I wanted a test harness that could run the original version of the program (call it launch_rockets.pl) and collect the standard output, but somehow skip the system calls that occur inside launch_rockets.pl. The following code successfully overrides system inside launch_rockets.pl: 

use subs qw(system); 
my $SYSTEM_SUCCESS = 0; 
sub system { 
    print "***\n"; 
    print "system @_\n"; 
    print "***\n\n"; 
    return $SYSTEM_SUCCESS; 
} 
local @ARGV = @test_args; 
do 'launch_rockets.pl';

[download]

So far so good. But launch_rockets.pl also contains 

use Proc::Background;

[download]
and later 
Proc::Background->new('perl', 'launch_missiles.pl');

[download]

I could copy launch_rockets.pl into a sandbox where Proc::Background is replaced by a stub, but I was wondering if there was any override strategy that would be effective inside a do FILE call in the file's original environment.

In reply to Overriding a module that is used by a program I'm testing by Narveson

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.