Refactor perl sub for testability

Question

I have inherited a perl code base. Consider the following subroutine;

sub getSysRTable
{
    my $iface = shift;
    return if not length($iface);
    my %ip_routes;
    my @routes = `/usr/bin/netstat -rn`;
    foreach my $route(@routes) {
        if ($route =~ /([\S.]+)\s+([\d.]+.[\d.]+.[\d.]+.[\d.]+)\s+(UGS|UGHS)\s+($iface)/ )
            { $ip_routes {$1} = $2 }
    }
    return %ip_routes;
}

I want to write unit tests for this code. The testing I have in mind will use sample output from netstat -rn and check for expected behaviour. The sub as is, invokes a command, so injecting my test data is problematic with this implementation.

What is the idiomatic perlish approach to refactoring this sub for testability?

See [How do I mock Perl's built-in backticks operator?](http://stackoverflow.com/q/3678655/176646) — ThisSuitIsBlackNot, May 10 '16 at 17:17
Also, on *nix `netstat -r` just pulls data from /proc/net/route, so you could just parse it directly. — ThisSuitIsBlackNot, May 10 '16 at 17:50

score 5 · Answer 1 · answered May 10 '16 at 17:34

First, change your code as follows:

sub getDataForSysRTable {
    return `/usr/bin/netstat -rn`;
}

sub getSysRTable
{
    my $iface = shift;
    return if not length($iface);
    my %ip_routes;
    my @routes = getDataForSysRTable();
    foreach my $route(@routes) {
        if ($route =~ /([\S.]+)\s+([\d.]+.[\d.]+.[\d.]+.[\d.]+)\s+(UGS|UGHS)\s+($iface)/ )
            { $ip_routes {$1} = $2 }
    }
    return %ip_routes;
}

Then for your test, you can do

local *getDataForSysRTable = sub { 
   ... return known data ...
};

my $ip_routes = getSysRTable($iface);

For mocking subroutines I prefer to use http://search.cpan.org/~gfranks/Test-MockModule-0.11/lib/Test/MockModule.pm — bart, May 10 '16 at 20:42

Refactor perl sub for testability

1 Answers1