diff --git a/src/main/java/ovh/gasser/newshapes/ui/visitors/HTMLDraftman.java b/src/main/java/ovh/gasser/newshapes/ui/visitors/HTMLDraftman.java
index 0a1419d..ea376e9 100644
--- a/src/main/java/ovh/gasser/newshapes/ui/visitors/HTMLDraftman.java
+++ b/src/main/java/ovh/gasser/newshapes/ui/visitors/HTMLDraftman.java
@@ -66,11 +66,11 @@ public class HTMLDraftman implements ShapeVisitor {
 
     @Override
     public void visitTriangle(STriangle sTriangle) {
-        htmlOutput.printf("<div class=\"triangle%d\"></div>\n", this.hashCode());
+        htmlOutput.printf("<div class=\"triangle%d\"></div>\n", sTriangle.hashCode());
         var bounds = sTriangle.getBounds();
         ColorAttributes colAttrs = (ColorAttributes) sTriangle.getAttributes(ColorAttributes.ID);
         String colorString = formatCSSColor(colAttrs.filledColor);
-        StringJoiner joiner = new StringJoiner("\n", ".triangle%d{\n".formatted(this.hashCode()), "\n}\n");
+        StringJoiner joiner = new StringJoiner("\n", ".triangle%d{\n".formatted(sTriangle.hashCode()), "\n}\n");
         joiner.add("  position: absolute;");
         joiner.add("  top: %dpx;".formatted(bounds.y));
         joiner.add("  left: %dpx;".formatted(bounds.x));
diff --git a/src/test/java/ovh/gasser/newshapes/SelectionTest.java b/src/test/java/ovh/gasser/newshapes/SelectionTest.java
new file mode 100644
index 0000000..6e49d6d
--- /dev/null
+++ b/src/test/java/ovh/gasser/newshapes/SelectionTest.java
@@ -0,0 +1,144 @@
+package ovh.gasser.newshapes;
+
+import org.junit.jupiter.api.Test;
+import ovh.gasser.newshapes.attributes.SelectionAttributes;
+import ovh.gasser.newshapes.shapes.SCircle;
+import ovh.gasser.newshapes.shapes.SRectangle;
+import ovh.gasser.newshapes.shapes.STriangle;
+import ovh.gasser.newshapes.ui.listeners.SelectionListener;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class SelectionTest {
+
+    @Test
+    void testIsEmptyInitially() {
+        Selection selection = new Selection();
+        assertTrue(selection.isEmpty());
+    }
+
+    @Test
+    void testAdd() {
+        Selection selection = new Selection();
+        SCircle circle = SCircle.create(0, 0, 50);
+
+        selection.add(circle);
+
+        assertFalse(selection.isEmpty());
+        assertEquals(1, selection.getSelectedShapes().size());
+        assertTrue(selection.getSelectedShapes().contains(circle));
+
+        // Verify shape is marked as selected
+        SelectionAttributes attrs = (SelectionAttributes) circle.getAttributes(SelectionAttributes.ID);
+        assertNotNull(attrs);
+        assertTrue(attrs.selected);
+    }
+
+    @Test
+    void testAddAll() {
+        Selection selection = new Selection();
+        SCircle circle1 = SCircle.create(0, 0, 50);
+        SRectangle rect = SRectangle.create(10, 10, 100, 50);
+        STriangle triangle = STriangle.create(50, 50, 30, java.awt.Color.BLACK, java.awt.Color.BLACK);
+
+        List<ovh.gasser.newshapes.shapes.Shape> shapes = Arrays.asList(circle1, rect, triangle);
+        selection.addAll(shapes);
+
+        assertEquals(3, selection.getSelectedShapes().size());
+        assertTrue(selection.getSelectedShapes().contains(circle1));
+        assertTrue(selection.getSelectedShapes().contains(rect));
+        assertTrue(selection.getSelectedShapes().contains(triangle));
+    }
+
+    @Test
+    void testClear() {
+        Selection selection = new Selection();
+        SCircle circle = SCircle.create(0, 0, 50);
+        SRectangle rect = SRectangle.create(10, 10, 100, 50);
+
+        selection.add(circle);
+        selection.add(rect);
+
+        assertFalse(selection.isEmpty());
+        assertEquals(2, selection.getSelectedShapes().size());
+
+        selection.clear();
+
+        assertTrue(selection.isEmpty());
+        assertEquals(0, selection.getSelectedShapes().size());
+
+        // Verify shapes are marked as unselected
+        SelectionAttributes circleAttrs = (SelectionAttributes) circle.getAttributes(SelectionAttributes.ID);
+        SelectionAttributes rectAttrs = (SelectionAttributes) rect.getAttributes(SelectionAttributes.ID);
+
+        assertNotNull(circleAttrs);
+        assertNotNull(rectAttrs);
+        assertFalse(circleAttrs.selected);
+        assertFalse(rectAttrs.selected);
+    }
+
+    @Test
+    void testGetSelectedShapesReturnsCopy() {
+        Selection selection = new Selection();
+        SCircle circle = SCircle.create(0, 0, 50);
+        selection.add(circle);
+
+        List<ovh.gasser.newshapes.shapes.Shape> copy = selection.getSelectedShapes();
+
+        // Try to modify the copy
+        assertThrows(UnsupportedOperationException.class, () -> copy.add(SCircle.create(10, 10, 20)));
+
+        // Original should be unchanged
+        assertEquals(1, selection.getSelectedShapes().size());
+    }
+
+    @Test
+    void testAddListener() {
+        Selection selection = new Selection();
+        AtomicBoolean listenerNotified = new AtomicBoolean(false);
+        AtomicInteger notificationCount = new AtomicInteger(0);
+
+        SelectionListener listener = (selectedShapes) -> {
+            listenerNotified.set(true);
+            notificationCount.incrementAndGet();
+        };
+
+        selection.addListener(listener);
+
+        // Adding a shape should notify listener
+        SCircle circle = SCircle.create(0, 0, 50);
+        selection.add(circle);
+
+        assertTrue(listenerNotified.get());
+        assertEquals(1, notificationCount.get());
+
+        // Adding another shape should notify listener again
+        SRectangle rect = SRectangle.create(10, 10, 100, 50);
+        selection.add(rect);
+
+        assertEquals(2, notificationCount.get());
+
+        // Clearing should notify listener
+        selection.clear();
+
+        assertEquals(3, notificationCount.get());
+    }
+
+    @Test
+    void testNullAddAllDoesNothing() {
+        Selection selection = new Selection();
+
+        // Should not throw
+        assertDoesNotThrow(() -> selection.addAll(null));
+
+        // Selection should still be empty
+        assertTrue(selection.isEmpty());
+    }
+}
diff --git a/src/test/java/ovh/gasser/newshapes/shapes/SCollectionTest.java b/src/test/java/ovh/gasser/newshapes/shapes/SCollectionTest.java
new file mode 100644
index 0000000..fa69168
--- /dev/null
+++ b/src/test/java/ovh/gasser/newshapes/shapes/SCollectionTest.java
@@ -0,0 +1,176 @@
+package ovh.gasser.newshapes.shapes;
+
+import org.junit.jupiter.api.Test;
+import ovh.gasser.newshapes.App;
+import ovh.gasser.newshapes.attributes.ColorAttributes;
+import ovh.gasser.newshapes.attributes.SelectionAttributes;
+
+import java.awt.Color;
+import java.awt.Rectangle;
+import java.util.Iterator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class SCollectionTest {
+
+    @Test
+    void testCreateWithShapes() {
+        SRectangle rect = SRectangle.create(10, 20, 100, 50);
+        SCircle circle = SCircle.create(50, 50, 25);
+        
+        SCollection collection = SCollection.of(rect, circle);
+        
+        assertNotNull(collection);
+        assertEquals(2, collection.stream().count());
+    }
+
+    @Test
+    void testAdd() {
+        SCollection collection = SCollection.of();
+        SRectangle rect = SRectangle.create(10, 20, 100, 50);
+        
+        collection.add(rect);
+        
+        assertEquals(1, collection.stream().count());
+        assertSame(rect, collection.iterator().next());
+    }
+
+    @Test
+    void testRemove() {
+        SRectangle rect = SRectangle.create(10, 20, 100, 50);
+        SCollection collection = SCollection.of(rect);
+        
+        collection.remove(rect);
+        
+        assertEquals(0, collection.stream().count());
+    }
+
+    @Test
+    void testIterator() {
+        SRectangle rect1 = SRectangle.create(10, 20, 100, 50);
+        SRectangle rect2 = SRectangle.create(30, 40, 60, 70);
+        SCollection collection = SCollection.of(rect1, rect2);
+        
+        Iterator<Shape> iterator = collection.iterator();
+        
+        assertTrue(iterator.hasNext());
+        assertSame(rect1, iterator.next());
+        assertTrue(iterator.hasNext());
+        assertSame(rect2, iterator.next());
+        assertFalse(iterator.hasNext());
+    }
+
+    @Test
+    void testStream() {
+        SRectangle rect1 = SRectangle.create(10, 20, 100, 50);
+        SRectangle rect2 = SRectangle.create(30, 40, 60, 70);
+        SCircle circle = SCircle.create(50, 50, 25);
+        SCollection collection = SCollection.of(rect1, rect2, circle);
+        
+        List<Shape> shapes = collection.stream().collect(Collectors.toList());
+        
+        assertEquals(3, shapes.size());
+        assertTrue(shapes.contains(rect1));
+        assertTrue(shapes.contains(rect2));
+        assertTrue(shapes.contains(circle));
+    }
+
+    @Test
+    void testGetBoundsEmptyCollection() {
+        SCollection collection = SCollection.of();
+        
+        Rectangle bounds = collection.getBounds();
+        
+        assertEquals(App.WIN_SIZE.width, bounds.width);
+        assertEquals(App.WIN_SIZE.height, bounds.height);
+    }
+
+    @Test
+    void testGetBoundsWithChildren() {
+        SRectangle rect1 = SRectangle.create(10, 10, 50, 50);
+        SRectangle rect2 = SRectangle.create(100, 100, 80, 40);
+        SCollection collection = SCollection.of(rect1, rect2);
+        
+        Rectangle bounds = collection.getBounds();
+        
+        // Union should cover from (10,10) to (180,140)
+        assertEquals(10, bounds.x);
+        assertEquals(10, bounds.y);
+        assertEquals(170, bounds.width);  // 100+80-10 = 170
+        assertEquals(130, bounds.height); // 100+40-10 = 130
+    }
+
+    @Test
+    void testTranslate() {
+        SRectangle rect = SRectangle.create(10, 20, 100, 50);
+        SCollection collection = SCollection.of(rect);
+        
+        collection.translate(5, 10);
+        
+        Rectangle bounds = rect.getBounds();
+        assertEquals(15, bounds.x);
+        assertEquals(30, bounds.y);
+    }
+
+    @Test
+    void testClone() {
+        SRectangle rect = SRectangle.create(10, 20, 100, 50);
+        SCollection original = SCollection.of(rect);
+        
+        SCollection cloned = (SCollection) original.clone();
+        
+        assertNotSame(original, cloned);
+        assertEquals(original.stream().count(), cloned.stream().count());
+        
+        // Verify SelectionAttributes is added to clone
+        assertNotNull(cloned.getAttributes(SelectionAttributes.ID));
+        
+        // Verify deep copy - modifying clone doesn't affect original
+        Iterator<Shape> clonedIterator = cloned.iterator();
+        Shape clonedChild = clonedIterator.next();
+        clonedChild.translate(100, 100);
+        
+        Rectangle originalBounds = rect.getBounds();
+        assertEquals(10, originalBounds.x);
+        assertEquals(20, originalBounds.y);
+    }
+
+    @Test
+    void testToString() {
+        SCollection collection = SCollection.of();
+        
+        String str = collection.toString();
+        
+        assertTrue(str.contains("SCollection"));
+    }
+
+    @Test
+    void testAddAttributesPropagatesToChildren() {
+        SRectangle rect = SRectangle.create(10, 20, 100, 50);
+        SCollection collection = SCollection.of(rect);
+        
+        ColorAttributes attrs = new ColorAttributes(true, true, Color.RED, Color.BLUE);
+        collection.addAttributes(attrs);
+        
+        ColorAttributes childAttrs = (ColorAttributes) rect.getAttributes(ColorAttributes.ID);
+        
+        assertNotNull(childAttrs);
+        assertEquals(Color.RED, childAttrs.filledColor);
+        assertEquals(Color.BLUE, childAttrs.strokedColor);
+    }
+
+    @Test
+    void testGetAttributesReturnsChildColor() {
+        SRectangle rect = SRectangle.create(10, 20, 100, 50, Color.GREEN);
+        SCircle circle = SCircle.create(50, 50, 25);
+        SCollection collection = SCollection.of(rect, circle);
+        
+        ColorAttributes attrs = (ColorAttributes) collection.getAttributes(ColorAttributes.ID);
+        
+        assertNotNull(attrs);
+        // First child's color should be returned (strokedColor for SRectangle)
+        assertEquals(Color.GREEN, attrs.strokedColor);
+    }
+}
diff --git a/src/test/java/ovh/gasser/newshapes/util/StreamableTest.java b/src/test/java/ovh/gasser/newshapes/util/StreamableTest.java
new file mode 100644
index 0000000..1b01a05
--- /dev/null
+++ b/src/test/java/ovh/gasser/newshapes/util/StreamableTest.java
@@ -0,0 +1,48 @@
+package ovh.gasser.newshapes.util;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class StreamableTest {
+
+    private static class TestStreamable implements Streamable<String> {
+        private final List<String> elements;
+
+        TestStreamable(List<String> elements) {
+            this.elements = new ArrayList<>(elements);
+        }
+
+        @Override
+        public java.util.Iterator<String> iterator() {
+            return elements.iterator();
+        }
+    }
+
+    @Test
+    void testStreamReturnsStreamOfElements() {
+        List<String> testData = Arrays.asList("a", "b", "c");
+        Streamable<String> streamable = new TestStreamable(testData);
+
+        Stream<String> result = streamable.stream();
+
+        assertNotNull(result);
+        assertEquals(testData, result.toList());
+    }
+
+    @Test
+    void testStreamEmptyCollection() {
+        List<String> emptyData = new ArrayList<>();
+        Streamable<String> streamable = new TestStreamable(emptyData);
+
+        Stream<String> result = streamable.stream();
+
+        assertNotNull(result);
+        assertTrue(result.toList().isEmpty());
+    }
+}