feat: Implement intro screen with retro 80s aesthetic and unit tests

tests/unit/intro.test.js

@@ -0,0 +1,85 @@
+const IntroScreen = require('../../src/js/screens/intro');
+
+describe('IntroScreen', () => {
+    let introScreen;
+
+    beforeEach(() => {
+        introScreen = new IntroScreen();
+    });
+
+    describe('constructor', () => {
+        it('should initialize with correct default values', () => {
+            expect(introScreen.title).toBe('WINGS88');
+            expect(introScreen.credits).toBe('A RetroWeb Games Production');
+            expect(introScreen.instructions).toBe('Use arrow keys to fly\nPress SPACE to start');
+            expect(introScreen.options).toEqual(['Start Game', 'Instructions', 'Quit']);
+            expect(introScreen.selectedOption).toBe(0);
+            expect(introScreen.audioContext).toBeNull();
+            expect(introScreen.musicTrack).toBeNull();
+        });
+    });
+
+    describe('moveSelection', () => {
+        it('should move selection up', () => {
+            introScreen.selectedOption = 1;
+            // Mock render to prevent DOM access
+            introScreen.render = jest.fn();
+            introScreen.moveSelection(-1);
+            expect(introScreen.selectedOption).toBe(0);
+            expect(introScreen.render).toHaveBeenCalled();
+        });
+
+        it('should move selection down', () => {
+            introScreen.selectedOption = 0;
+            // Mock render to prevent DOM access
+            introScreen.render = jest.fn();
+            introScreen.moveSelection(1);
+            expect(introScreen.selectedOption).toBe(1);
+            expect(introScreen.render).toHaveBeenCalled();
+        });
+
+        it('should wrap around from last to first', () => {
+            introScreen.selectedOption = 2;
+            // Mock render to prevent DOM access
+            introScreen.render = jest.fn();
+            introScreen.moveSelection(1);
+            expect(introScreen.selectedOption).toBe(0);
+            expect(introScreen.render).toHaveBeenCalled();
+        });
+
+        it('should wrap around from first to last', () => {
+            introScreen.selectedOption = 0;
+            // Mock render to prevent DOM access
+            introScreen.render = jest.fn();
+            introScreen.moveSelection(-1);
+            expect(introScreen.selectedOption).toBe(2);
+            expect(introScreen.render).toHaveBeenCalled();
+        });
+    });
+
+    describe('selectOption', () => {
+        it('should handle Start Game selection', () => {
+            introScreen.selectedOption = 0;
+            const logSpy = jest.spyOn(console, 'log');
+            introScreen.selectOption();
+            expect(logSpy).toHaveBeenCalledWith('Starting game...');
+            logSpy.mockRestore();
+        });
+
+        it('should handle Instructions selection', () => {
+            introScreen.selectedOption = 1;
+            const logSpy = jest.spyOn(console, 'log');
+            introScreen.selectOption();
+            expect(logSpy).toHaveBeenCalledWith('Showing instructions...');
+            logSpy.mockRestore();
+        });
+
+        it('should handle Quit selection', () => {
+            introScreen.selectedOption = 2;
+            const logSpy = jest.spyOn(console, 'log');
+            introScreen.selectOption();
+            expect(logSpy).toHaveBeenCalledWith('Quitting game...');
+            logSpy.mockRestore();
+        });
+    });
+});