test: add core unit tests

- Add JUnit 5 Jupiter dependencies to pom.xml
- Add maven-surefire-plugin for test execution
- Add AbstractShapeTest for base class methods
- Add SCircleTest, SRectangleTest, STriangleTest, STextTest

Tests cover: creation, bounds, clone, resize (AbstractShape)

src/test/java/ovh/gasser/newshapes/shapes/STextTest.java

@@ -0,0 +1,47 @@
+package ovh.gasser.newshapes.shapes;
+
+import org.junit.jupiter.api.Test;
+import java.awt.Font;
+import java.awt.Rectangle;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class STextTest {
+    @Test
+    void testCreate() {
+        SText text = SText.create(10, 20, "Hello");
+        assertNotNull(text);
+        assertEquals("Hello", text.getText());
+    }
+
+    @Test
+    void testCreateWithDefaultValues() {
+        SText text = SText.create(0, 0, "Test");
+        assertEquals("Test", text.getText());
+        assertEquals(SText.DEFAULT_FONT_SIZE, text.getFontSize());
+        assertEquals(SText.DEFAULT_FONT_NAME, text.getFontName());
+        assertEquals(SText.DEFAULT_FONT_STYLE, text.getFontStyle());
+    }
+
+    @Test
+    void testCloneCreatesIndependentCopy() {
+        SText original = SText.create(5, 5, "Copy");
+        Object cloneObj = original.clone();
+        assertNotSame(original, cloneObj);
+        assertTrue(cloneObj instanceof SText);
+        SText clone = (SText) cloneObj;
+        assertEquals(original.getText(), clone.getText());
+    }
+
+    @Test
+    void testPlaceholderTextForEmpty() {
+        SText text = SText.create(0, 0, "");
+        assertEquals(SText.PLACEHOLDER_TEXT, text.getText());
+    }
+
+    @Test
+    void testPlaceholderTextForNull() {
+        SText text = SText.create(0, 0, null);
+        assertEquals(SText.PLACEHOLDER_TEXT, text.getText());
+    }
+}