Added MenuManager class with select function with test.

src/main/java/Application/MenuManager.java

@@ -0,0 +1,22 @@
+package Application;
+
+public class MenuManager {
+
+    private Menu rootMenu;
+    private Menu currentMenu;
+
+    public MenuManager(Menu rootMenu){
+        this.rootMenu = rootMenu;
+        this.currentMenu = rootMenu;
+    }
+
+    public void select(int i){
+        this.currentMenu = currentMenu.getMenu(i);
+    }
+
+    public Menu getCurrentMenu(){
+        return this.currentMenu;
+    }
+
+
+}

src/test/java/Application/MenuManagerTest.java

@@ -0,0 +1,38 @@
+package Application;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class MenuManagerTest {
+
+    MenuManager mm;
+    Menu rootMenu;
+
+    @BeforeEach
+    void setUp() {
+        rootMenu = new Menu("Root");
+        Menu menu1 = new Menu("Menu1");
+        Menu menu2 = new Menu("Menu2");
+        Menu menu1_1 = new Menu("Menu1.1");
+        menu1.addMenu(menu1_1);
+        rootMenu.addMenu(menu1);
+        rootMenu.addMenu(menu2);
+        mm = new MenuManager(rootMenu);
+    }
+
+    @AfterEach
+    void tearDown() {
+    }
+
+    @Test
+    void testSelectFunction(){
+        assertEquals(mm.getCurrentMenu(), rootMenu);
+        mm.select(0);
+        assertEquals(mm.getCurrentMenu(), rootMenu.getMenu(0));
+        mm.select(0);
+        assertEquals(mm.getCurrentMenu(), rootMenu.getMenu(0).getMenu(0));
+    }
+}