New unit test for layer heights

MANIFEST

@@ -59,6 +59,7 @@ t/custom_gcode.t
 t/dynamic.t
 t/fill.t
 t/geometry.t
+t/layers.t
 t/loops.t
 t/polyclip.t
 t/retraction.t

t/layers.t

@@ -0,0 +1,58 @@
+use Test::More tests => 4;
+use strict;
+use warnings;
+
+BEGIN {
+    use FindBin;
+    use lib "$FindBin::Bin/../lib";
+}
+
+use List::Util qw(first);
+use Slic3r;
+use Slic3r::Test qw(_eq);
+
+my $config = Slic3r::Config->new_from_defaults;
+
+my $test = sub {
+    my ($conf) = @_;
+    $conf ||= $config;
+
+    my $print = Slic3r::Test::init_print('20mm_cube', config => $conf);
+
+    my @z = ();
+    my @increments = ();
+    Slic3r::Test::GCodeReader->new(gcode => Slic3r::Test::gcode($print))->parse(sub {
+        my ($self, $cmd, $args, $info) = @_;
+
+        if ($info->{dist_Z}) {
+            push @z, 1*$args->{Z};
+            push @increments, $info->{dist_Z};
+        }
+    });
+
+    fail 'wrong first layer height'
+        if $z[0] ne $config->get_value('first_layer_height') + $config->z_offset;
+
+    fail 'wrong second layer height'
+        if $z[1] ne $config->get_value('first_layer_height') + $config->get_value('layer_height') + $config->z_offset;
+
+    fail 'wrong layer height'
+        if first { !_eq($_, $config->layer_height) } @increments[1..$#increments];
+
+    1;
+};
+
+$config->set('layer_height', 0.3);
+$config->set('first_layer_height', 0.2);
+ok $test->(), "absolute first layer height";
+
+$config->set('first_layer_height', '60%');
+ok $test->(), "relative first layer height";
+
+$config->set('z_offset', 0.9);
+ok $test->(), "positive Z offset";
+
+$config->set('z_offset', -0.8);
+ok $test->(), "negative Z offset";
+
+__END__