diff --git a/t/shells.t b/t/shells.t
deleted file mode 100644
index cf6a7dce9..000000000
--- a/t/shells.t
+++ /dev/null
@@ -1,268 +0,0 @@
-use Test::More tests => 17;
-use strict;
-use warnings;
-
-BEGIN {
-    use FindBin;
-    use lib "$FindBin::Bin/../lib";
-    use local::lib "$FindBin::Bin/../local-lib";
-}
-
-use List::Util qw(first sum);
-use Slic3r;
-use Slic3r::Geometry qw(epsilon);
-use Slic3r::Test;
-
-# issue #1161
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    $config->set('layer_height', 0.3);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('bottom_solid_layers', 0);
-    $config->set('top_solid_layers', 3);
-    $config->set('cooling', [ 0 ]);
-    $config->set('bridge_speed', 99);
-    $config->set('solid_infill_speed', 99);
-    $config->set('top_solid_infill_speed', 99);
-    $config->set('first_layer_speed', '100%');
-    $config->set('enable_dynamic_overhang_speeds', 0);  # prevent speed alteration
-    
-    my $print = Slic3r::Test::init_print('V', config => $config);
-    my %layers_with_solid_infill = ();  # Z => 1
-    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-        my ($self, $cmd, $args, $info) = @_;
-        
-        $layers_with_solid_infill{$self->Z} = 1
-            if $info->{extruding} && ($args->{F} // $self->F) == $config->solid_infill_speed*60;
-    });
-    is scalar(map $layers_with_solid_infill{$_}, grep $_ <= 7.2, keys %layers_with_solid_infill), 3,
-        "correct number of top solid shells is generated in V-shaped object";
-}
-
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    # we need to check against one perimeter because this test is calibrated
-    # (shape, extrusion_width) so that perimeters cover the bottom surfaces of
-    # their lower layer - the test checks that shells are not generated on the
-    # above layers (thus 'across' the shadow perimeter)
-    # the test is actually calibrated to leave a narrow bottom region for each
-    # layer - we test that in case of fill_density = 0 such narrow shells are 
-    # discarded instead of grown
-    $config->set('perimeters', 1);
-    $config->set('fill_density', 0);
-    $config->set('cooling', [ 0 ]);             # prevent speed alteration
-    $config->set('first_layer_speed', '100%');  # prevent speed alteration
-    $config->set('enable_dynamic_overhang_speeds', 0);  # prevent speed alteration
-    $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('extrusion_width', 0.55);
-    $config->set('bottom_solid_layers', 3);
-    $config->set('top_solid_layers', 0);
-    $config->set('solid_infill_speed', 99);
-    
-    my $print = Slic3r::Test::init_print('V', config => $config);
-    my %layers = ();  # Z => 1
-    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-        my ($self, $cmd, $args, $info) = @_;
-        $layers{$self->Z} = 1
-            if $info->{extruding} && ($args->{F} // $self->F) == $config->solid_infill_speed*60;
-    });
-    is scalar(keys %layers), $config->bottom_solid_layers,
-        "shells are not propagated across perimeters of the neighbor layer";
-}
-
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    $config->set('perimeters', 3);
-    $config->set('cooling', [ 0 ]);             # prevent speed alteration
-    $config->set('first_layer_speed', '100%');  # prevent speed alteration
-    $config->set('enable_dynamic_overhang_speeds', 0);  # prevent speed alteration
-    $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('bottom_solid_layers', 3);
-    $config->set('top_solid_layers', 3);
-    $config->set('solid_infill_speed', 99);
-    $config->set('top_solid_infill_speed', 99);
-    $config->set('bridge_speed', 99);
-    $config->set('filament_diameter', [ 3.0 ]);
-    $config->set('nozzle_diameter', [ 0.5 ]);
-
-    my $print = Slic3r::Test::init_print('sloping_hole', config => $config);
-    my %solid_layers = ();  # Z => 1
-    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-        my ($self, $cmd, $args, $info) = @_;
-        $solid_layers{$self->Z} = 1
-            if $info->{extruding} && ($args->{F} // $self->F) == $config->solid_infill_speed*60;
-    });
-    is scalar(keys %solid_layers), $config->bottom_solid_layers + $config->top_solid_layers,
-        "no superfluous shells are generated";
-}
-
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    $config->set('perimeters', 1);
-    $config->set('fill_density', 0);
-    $config->set('top_solid_layers', 0);
-    $config->set('spiral_vase', 1);
-    $config->set('bottom_solid_layers', 0);
-    $config->set('skirts', 0);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('start_gcode', '');
-    $config->set('temperature', [200]);
-    $config->set('first_layer_temperature', [205]);
-    
-    # TODO: this needs to be tested with a model with sloping edges, where starting
-    # points of each layer are not aligned - in that case we would test that no
-    # travel moves are left to move to the new starting point - in a cube, end
-    # points coincide with next layer starting points (provided there's no clipping)
-    my $test = sub {
-        my ($model_name, $description) = @_;
-        my $print = Slic3r::Test::init_print($model_name, config => $config);
-        my $travel_moves_after_first_extrusion = 0;
-        my $started_extruding = 0;
-        my $first_layer_temperature_set = 0;
-        my $temperature_set = 0;
-        my @z_steps = ();
-        Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-            my ($self, $cmd, $args, $info) = @_;
-            
-            if ($cmd eq 'G1') {
-                $started_extruding = 1 if $info->{extruding};
-                push @z_steps, $info->{dist_Z}
-                    if $started_extruding && $info->{dist_Z} > 0;
-                $travel_moves_after_first_extrusion++
-                    if $info->{travel} && $info->{dist_XY} > 0 && $started_extruding && !exists $args->{Z};
-            } elsif ($cmd eq 'M104') {
-                $first_layer_temperature_set = 1 if $args->{S} == 205;
-                $temperature_set = 1 if $args->{S} == 200;
-            }
-        });
-        
-        ok $first_layer_temperature_set, 'first layer temperature is preserved';
-        ok $temperature_set, 'temperature is preserved';
-        
-        # we allow one travel move after first extrusion: i.e. when moving to the first
-        # spiral point after moving to second layer (bottom layer had loop clipping, so
-        # we're slightly distant from the starting point of the loop)
-        ok $travel_moves_after_first_extrusion <= 1, "no gaps in spiral vase ($description)";
-        ok !(grep { $_ > $config->layer_height + epsilon } @z_steps), "no gaps in Z ($description)";
-    };
-    
-    $test->('20mm_cube', 'solid model');
-    
-    $config->set('z_offset', -10);
-    $test->('20mm_cube', 'solid model with negative z-offset');
-    
-    ### Disabled because the current unreliable medial axis code doesn't
-    ### always produce valid loops.
-    ###$test->('40x10', 'hollow model with negative z-offset');
-}
-
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    $config->set('spiral_vase', 1);
-    $config->set('perimeters', 1);
-    $config->set('fill_density', 0);
-    $config->set('top_solid_layers', 0);
-    $config->set('bottom_solid_layers', 0);
-    $config->set('retract_layer_change', [0]);
-    $config->set('skirts', 0);
-    $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('start_gcode', '');
-#    $config->set('use_relative_e_distances', 1);
-    $config->validate;
-    
-    my $print = Slic3r::Test::init_print('20mm_cube', config => $config);
-    my $z_moves = 0;
-    my @this_layer = ();  # [ dist_Z, dist_XY ], ...
-    
-    my $bottom_layer_not_flat = 0;
-    my $null_z_moves_not_layer_changes = 0;
-    my $null_z_moves_not_multiples_of_layer_height = 0;
-    my $sum_of_partial_z_equals_to_layer_height = 0;
-    my $all_layer_segments_have_same_slope = 0;
-    my $horizontal_extrusions = 0;
-    
-    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-        my ($self, $cmd, $args, $info) = @_;
-        
-        if ($cmd eq 'G1') {
-            if ($z_moves < 2) {
-                # skip everything up to the second Z move
-                # (i.e. start of second layer)
-                if (exists $args->{Z}) {
-                    $z_moves++;
-                    $bottom_layer_not_flat = 1
-                        if $info->{dist_Z} > 0 && $info->{dist_Z} != $config->layer_height;
-                }
-            } elsif ($info->{dist_Z} == 0 && $args->{Z}) {
-                $null_z_moves_not_layer_changes = 1
-                    if $info->{dist_XY} != 0;
-                
-                # % doesn't work easily with floats
-                $null_z_moves_not_multiples_of_layer_height = 1
-                    if abs(($args->{Z} / $config->layer_height) * $config->layer_height - $args->{Z}) > epsilon;
-                
-                my $total_dist_XY = sum(map $_->[1], @this_layer);
-                $sum_of_partial_z_equals_to_layer_height = 1
-                    if abs(sum(map $_->[0], @this_layer) - $config->layer_height) > 
-                        # The first segment on the 2nd layer has extrusion interpolated from zero 
-                        # and the 1st segment has such a low extrusion assigned, that it is effectively zero, thus the move
-                        # is considered non-extruding and a higher epsilon is required.
-                        ($z_moves == 2 ? 0.0021 : epsilon);
-                #printf ("Total height: %f, layer height: %f, good: %d\n", sum(map $_->[0], @this_layer), $config->layer_height, $sum_of_partial_z_equals_to_layer_height);
-                
-                foreach my $segment (@this_layer) {
-                    # check that segment's dist_Z is proportioned to its dist_XY
-                    $all_layer_segments_have_same_slope = 1
-                        if abs($segment->[0]*$total_dist_XY/$config->layer_height - $segment->[1]) > 0.2;
-                }
-                
-                @this_layer = ();
-            } elsif ($info->{extruding} && $info->{dist_XY} > 0) {
-                $horizontal_extrusions = 1
-                    if $info->{dist_Z} == 0;
-                #printf("Pushing dist_z: %f, dist_xy: %f\n", $info->{dist_Z}, $info->{dist_XY});
-                push @this_layer, [ $info->{dist_Z}, $info->{dist_XY} ];
-            }
-        }
-    });
-    ok !$bottom_layer_not_flat, 'bottom layer is flat when using spiral vase';
-    ok !$null_z_moves_not_layer_changes, 'null Z moves are layer changes';
-    ok !$null_z_moves_not_multiples_of_layer_height, 'null Z moves are multiples of layer height';
-    ok !$sum_of_partial_z_equals_to_layer_height, 'sum of partial Z increments equals to a full layer height';
-    ok !$all_layer_segments_have_same_slope, 'all layer segments have the same slope';
-    ok !$horizontal_extrusions, 'no horizontal extrusions';
-}
-
-# The current Spiral Vase slicing code removes the holes and all but the largest contours from each slice,
-# therefore the following test is no more valid.
-#{
-#    my $config = Slic3r::Config::new_from_defaults;
-#    $config->set('perimeters', 1);
-#    $config->set('fill_density', 0);
-#    $config->set('top_solid_layers', 0);
-#    $config->set('spiral_vase', 1);
-#    $config->set('bottom_solid_layers', 0);
-#    $config->set('skirts', 0);
-#    $config->set('first_layer_height', $config->layer_height);
-#    $config->set('start_gcode', '');
-#    
-#    my $print = Slic3r::Test::init_print('two_hollow_squares', config => $config);
-#    my $diagonal_moves = 0;
-#    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-#        my ($self, $cmd, $args, $info) = @_;
-#        
-#        if ($cmd eq 'G1') {
-#            if ($info->{extruding} && $info->{dist_XY} > 0) {
-#                if ($info->{dist_Z} > 0) {
-#                    $diagonal_moves++;
-#                }
-#            }
-#        }
-#    });
-#    is $diagonal_moves, 0, 'no spiral moves on two-island object';
-#}
-
-__END__
diff --git a/tests/fff_print/test_shells.cpp b/tests/fff_print/test_shells.cpp
index df0e8f6bb..d9e5817ca 100644
--- a/tests/fff_print/test_shells.cpp
+++ b/tests/fff_print/test_shells.cpp
@@ -9,16 +9,14 @@ using namespace Slic3r;
 
 SCENARIO("Shells", "[Shells]") {
     GIVEN("20mm box") {
-        auto test = [](const DynamicPrintConfig &config){
-            std::string gcode = Slic3r::Test::slice({ Slic3r::Test::TestMesh::cube_20x20x20 }, config);
-            
+        auto test = [](const DynamicPrintConfig &config){            
             std::vector<coord_t> zs;
             std::set<coord_t> layers_with_solid_infill;
             std::set<coord_t> layers_with_bridge_infill;
             const double solid_infill_speed = config.opt_float("solid_infill_speed") * 60;
             const double bridge_speed       = config.opt_float("bridge_speed") * 60;
             GCodeReader parser;
-            parser.parse_buffer(gcode,
+            parser.parse_buffer(Slic3r::Test::slice({ Slic3r::Test::TestMesh::cube_20x20x20 }, config),
                 [&zs, &layers_with_solid_infill, &layers_with_bridge_infill, solid_infill_speed, bridge_speed]
                     (Slic3r::GCodeReader &self, const Slic3r::GCodeReader::GCodeLine &line)
             {
@@ -110,3 +108,294 @@ SCENARIO("Shells", "[Shells]") {
         }
     }
 }
+
+static std::set<double> layers_with_speed(const std::string &gcode, int speed)
+{
+    std::set<double> out;
+    GCodeReader parser;
+    parser.parse_buffer(gcode, [&out, speed](Slic3r::GCodeReader &self, const Slic3r::GCodeReader::GCodeLine &line) {
+        if (line.extruding(self) && is_approx<double>(line.new_F(self), speed * 60.))
+            out.insert(self.z());
+    });
+    return out;
+}
+
+SCENARIO("Shells (from Perl)", "[Shells]") {
+    GIVEN("V shape, Slic3r GH #1161") {
+        int solid_speed = 99;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "layer_height",           0.3 },
+            { "first_layer_height",     0.3 },
+            { "bottom_solid_layers",    0 },
+            { "top_solid_layers",       3 },
+            // to prevent speeds from being altered
+            { "cooling",                "0" },
+            { "bridge_speed",           solid_speed },
+            { "solid_infill_speed",     solid_speed },
+            { "top_solid_infill_speed", solid_speed },
+            // to prevent speeds from being altered
+            { "first_layer_speed",      "100%" },
+            // prevent speed alteration
+            { "enable_dynamic_overhang_speeds", 0 }
+        });
+        
+        THEN("correct number of top solid shells is generated in V-shaped object") {
+            size_t n = 0;
+            for (auto z : layers_with_speed(Slic3r::Test::slice({TestMesh::V}, config), solid_speed))
+                if (z <= 7.2)
+                    ++ n;
+            REQUIRE(n == 3);
+        }
+    }
+    GIVEN("V shape") {
+        // we need to check against one perimeter because this test is calibrated
+        // (shape, extrusion_width) so that perimeters cover the bottom surfaces of
+        // their lower layer - the test checks that shells are not generated on the
+        // above layers (thus 'across' the shadow perimeter)
+        // the test is actually calibrated to leave a narrow bottom region for each
+        // layer - we test that in case of fill_density = 0 such narrow shells are 
+        // discarded instead of grown
+        int bottom_solid_layers = 3;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "perimeters",             1 },
+            { "fill_density",           0 },
+            // to prevent speeds from being altered
+            { "cooling",                "0" },
+            // to prevent speeds from being altered
+            { "first_layer_speed",      "100%" },
+            // prevent speed alteration
+            { "enable_dynamic_overhang_speeds", 0 },
+            { "layer_height",           0.4 },
+            { "first_layer_height",     0.4 },
+            { "extrusion_width",        0.55 },
+            { "bottom_solid_layers",    bottom_solid_layers },
+            { "top_solid_layers",       0 },
+            { "solid_infill_speed",     99 }
+        });
+        THEN("shells are not propagated across perimeters of the neighbor layer") {
+            std::string gcode = Slic3r::Test::slice({TestMesh::V}, config);
+            REQUIRE(layers_with_speed(gcode, 99).size() == bottom_solid_layers);
+        }
+    }
+    GIVEN("sloping_hole") {
+        int bottom_solid_layers = 3;
+        int top_solid_layers    = 3;
+        int solid_speed         = 99;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "perimeters",             3 },
+            // to prevent speeds from being altered
+            { "cooling",                "0" },
+            // to prevent speeds from being altered
+            { "first_layer_speed",      "100%" },
+            // prevent speed alteration
+            { "enable_dynamic_overhang_speeds", 0 },
+            { "layer_height",           0.4 },
+            { "first_layer_height",     0.4 },
+            { "bottom_solid_layers",    bottom_solid_layers },
+            { "top_solid_layers",       top_solid_layers },
+            { "solid_infill_speed",     solid_speed },
+            { "top_solid_infill_speed", solid_speed },
+            { "bridge_speed",           solid_speed },
+            { "filament_diameter",      3. },
+            { "nozzle_diameter",        0.5 }
+        });
+        THEN("no superfluous shells are generated") {
+            std::string gcode = Slic3r::Test::slice({TestMesh::sloping_hole}, config);
+            REQUIRE(layers_with_speed(gcode, solid_speed).size() == bottom_solid_layers + top_solid_layers);
+        }
+    }
+    GIVEN("20mm_cube, spiral vase") {
+        double layer_height = 0.3;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "perimeters",             1 },
+            { "fill_density",           0 },
+            { "layer_height",           layer_height },
+            { "first_layer_height",     layer_height },
+            { "top_solid_layers",       0 },
+            { "spiral_vase",            1 },
+            { "bottom_solid_layers",    0 },
+            { "skirts",                 0 },
+            { "start_gcode",            "" },
+            { "temperature",            200 },
+            { "first_layer_temperature", 205}
+        });
+        
+        // TODO: this needs to be tested with a model with sloping edges, where starting
+        // points of each layer are not aligned - in that case we would test that no
+        // travel moves are left to move to the new starting point - in a cube, end
+        // points coincide with next layer starting points (provided there's no clipping)
+        auto test = [layer_height](const DynamicPrintConfig &config) {
+            size_t              travel_moves_after_first_extrusion  = 0;
+            bool                started_extruding                   = false;
+            bool                first_layer_temperature_set         = false;
+            bool                temperature_set                     = false;
+            std::vector<double> z_steps;
+            GCodeReader         parser;
+            parser.parse_buffer(Slic3r::Test::slice({TestMesh::cube_20x20x20}, config), 
+                [&](Slic3r::GCodeReader &self, const Slic3r::GCodeReader::GCodeLine &line) {
+                if (line.cmd_is("G1")) {
+                    if (line.extruding(self))
+                        started_extruding = true;
+                    if (started_extruding) {
+                        if (double dz = line.dist_Z(self); dz > 0)
+                            z_steps.emplace_back(dz);
+                        if (line.travel() && line.dist_XY(self) > 0 && ! line.has(Z))
+                            ++ travel_moves_after_first_extrusion;
+                    }
+                } else if (line.cmd_is("M104")) {
+                    int s;
+                    if (line.has_value('S', s)) {
+                        if (s == 205)
+                            first_layer_temperature_set = true;
+                        else if (s == 200)
+                            temperature_set = true;
+                    }
+                }
+            });
+            THEN("first layer temperature is set") {
+                REQUIRE(first_layer_temperature_set);
+            }
+            THEN("temperature is set") {
+                REQUIRE(temperature_set);
+            }
+            // we allow one travel move after first extrusion: i.e. when moving to the first
+            // spiral point after moving to second layer (bottom layer had loop clipping, so
+            // we're slightly distant from the starting point of the loop)
+            THEN("no gaps in spiral vase") {
+                REQUIRE(travel_moves_after_first_extrusion <= 1);
+            }
+            THEN("no gaps in Z") {
+                REQUIRE(std::count_if(z_steps.begin(), z_steps.end(), 
+                    [&layer_height](auto z_step) { return z_step > layer_height + EPSILON; }) == 0);
+            }
+        };
+        WHEN("solid model") {
+            test(config);
+        }
+        WHEN("solid model with negative z-offset") {
+            config.set_deserialize_strict("z_offset", "-10");
+            test(config);
+        }
+        // Disabled because the current unreliable medial axis code doesn't always produce valid loops.
+        // $test->('40x10', 'hollow model with negative z-offset');
+    }
+    GIVEN("20mm_cube, spiral vase") {
+        double layer_height = 0.4;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "spiral_vase",            1 },
+            { "perimeters",             1 },
+            { "fill_density",           0 },
+            { "top_solid_layers",       0 },
+            { "bottom_solid_layers",    0 },
+            { "retract_layer_change",   0 },
+            { "skirts",                 0 },
+            { "layer_height",           layer_height },
+            { "first_layer_height",     layer_height },
+            { "start_gcode",            "" },
+            // { "use_relative_e_distances", 1}
+        });
+        config.validate();
+        
+        std::vector<std::pair<double, double>> this_layer; // [ dist_Z, dist_XY ], ...
+        int  z_moves                                    = 0;
+        bool bottom_layer_not_flat                      = false;
+        bool null_z_moves_not_layer_changes             = false;
+        bool null_z_moves_not_multiples_of_layer_height = false;
+        bool sum_of_partial_z_equals_to_layer_height    = false;
+        bool all_layer_segments_have_same_slope         = false;
+        bool horizontal_extrusions                      = false;
+        GCodeReader parser;
+        parser.parse_buffer(Slic3r::Test::slice({TestMesh::cube_20x20x20}, config), 
+            [&](Slic3r::GCodeReader &self, const Slic3r::GCodeReader::GCodeLine &line) {
+            if (line.cmd_is("G1")) {
+                if (z_moves < 2) {
+                    // skip everything up to the second Z move
+                    // (i.e. start of second layer)
+                    if (line.has(Z)) {
+                        ++ z_moves;
+                        if (double dz = line.dist_Z(self); dz > 0 && ! is_approx<double>(dz, layer_height))
+                            bottom_layer_not_flat = true;
+                    }
+                } else if (line.dist_Z(self) == 0 && line.has(Z)) {
+                    if (line.dist_XY(self) != 0)
+                        null_z_moves_not_layer_changes = true;
+                    double z = line.new_Z(self);
+                    if (fmod(z + EPSILON, layer_height) > 2 * EPSILON)
+                        null_z_moves_not_multiples_of_layer_height = true;
+                    double total_dist_XY = 0;
+                    double total_dist_Z  = 0;
+                    for (auto &seg : this_layer) {
+                        total_dist_Z  += seg.first;
+                        total_dist_XY += seg.second;
+                    }
+                    if (std::abs(total_dist_Z - layer_height) >
+                            // The first segment on the 2nd layer has extrusion interpolated from zero 
+                            // and the 1st segment has such a low extrusion assigned, that it is effectively zero, thus the move
+                            // is considered non-extruding and a higher epsilon is required.
+                            (z_moves == 2 ? 0.0021 : EPSILON))
+                        sum_of_partial_z_equals_to_layer_height = true;
+                    //printf("Total height: %f, layer height: %f, good: %d\n", sum(map $_->[0], @this_layer), $config->layer_height, $sum_of_partial_z_equals_to_layer_height);
+                    for (auto &seg : this_layer)
+                        // check that segment's dist_Z is proportioned to its dist_XY
+                        if (std::abs(seg.first * total_dist_XY / layer_height - seg.second) > 0.2)
+                            all_layer_segments_have_same_slope = true;
+                    this_layer.clear();
+                } else if (line.extruding(self) && line.dist_XY(self) > 0) {
+                    if (line.dist_Z(self) == 0)
+                        horizontal_extrusions = true;
+                    //printf("Pushing dist_z: %f, dist_xy: %f\n", $info->{dist_Z}, $info->{dist_XY});
+                    this_layer.emplace_back(line.dist_Z(self), line.dist_XY(self));
+                }
+            }
+        });
+        THEN("bottom layer is flat when using spiral vase") {
+            REQUIRE(! bottom_layer_not_flat);
+        }
+        THEN("null Z moves are layer changes") {
+            REQUIRE(! null_z_moves_not_layer_changes);
+        }
+        THEN("null Z moves are multiples of layer height") {
+            REQUIRE(! null_z_moves_not_multiples_of_layer_height);
+        }
+        THEN("sum of partial Z increments equals to a full layer height") {
+            REQUIRE(! sum_of_partial_z_equals_to_layer_height);
+        }
+        THEN("all layer segments have the same slope") {
+            REQUIRE(! all_layer_segments_have_same_slope);
+        }
+        THEN("no horizontal extrusions") {
+            REQUIRE(! horizontal_extrusions);
+        }
+    }
+}
+
+#if 0
+// The current Spiral Vase slicing code removes the holes and all but the largest contours from each slice,
+// therefore the following test is no more valid.
+{
+    my $config = Slic3r::Config::new_from_defaults;
+    $config->set('perimeters', 1);
+    $config->set('fill_density', 0);
+    $config->set('top_solid_layers', 0);
+    $config->set('spiral_vase', 1);
+    $config->set('bottom_solid_layers', 0);
+    $config->set('skirts', 0);
+    $config->set('first_layer_height', $config->layer_height);
+    $config->set('start_gcode', '');
+    
+    my $print = Slic3r::Test::init_print('two_hollow_squares', config => $config);
+    my $diagonal_moves = 0;
+    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
+        my ($self, $cmd, $args, $info) = @_;
+        
+        if ($cmd eq 'G1') {
+            if ($info->{extruding} && $info->{dist_XY} > 0) {
+                if ($info->{dist_Z} > 0) {
+                    $diagonal_moves++;
+                }
+            }
+        }
+    });
+    is $diagonal_moves, 0, 'no spiral moves on two-island object';
+}
+#endif