Add test for polyline lines

xs/t/09_polyline.t

@@ -0,0 +1,27 @@
+#!/usr/bin/perl
+
+use strict;
+use warnings;
+
+use Slic3r::XS;
+use Test::More tests => 4;
+
+my $points = [
+    [100, 100],
+    [200, 100],
+    [200, 200],
+];
+
+my $polyline = Slic3r::Polyline->new(@$points);
+is_deeply $polyline->pp, $points, 'polyline roundtrip';
+
+is ref($polyline->arrayref), 'ARRAY', 'polyline arrayref is unblessed';
+isa_ok $polyline->[0], 'Slic3r::Point', 'polyline point is blessed';
+
+my $lines = $polyline->lines;
+is_deeply [ map $_->pp, @$lines ], [
+    [ [100, 100], [200, 100] ],
+    [ [200, 100], [200, 200] ],
+], 'polyline lines';
+
+__END__