use strict;
use warnings;

my $s = 'This is a test';
my @pairs = $s =~ /(?=(\w+ \s+ \w+))\w+ \s+/gx;

print join "\n", @pairs;

##</code><code>##

This is
is a
a test

##</code><code>##

...
my @pairs = map [split], $s =~ /(?=(\w+ \s+ \w+))\w+ \s+/gx;

print "@$_\n" for @pairs;

##</code><code>##

This is
is a
a test