It's really a double loop.

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1128809

use strict;
use warnings;

while(<DATA>)
  {
  my @items;
  s/\s+/ /g; # simplify
  push @items, $1 =~ /, *(\w+)/g while /\btest \w+((?:, *\w+(?: is \w+
+)?)+)/g;
  @items and print "FOUND: @items\n";
  }

__DATA__
this line has nothing, nothing, nothing...
1 , 2, 3, 4 is four, 5, 6 test 00,11 is one,22,  33 is three,44,55 is 
+ the best, and  this  is not a test 111, 222, 333 as random  words to
+ finish
this should be a test, but nothing must be returned 4444, 7777, 9999 i
+s garbage
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