test: add main.tsx test coverage (#331)

Author: Hell1213

frontend/src/__tests__/main.test.tsx

@@ -0,0 +1,48 @@
+import React from 'react';
+import ReactDOM from 'react-dom/client';
+
+jest.mock('../App.tsx', () => ({
+  __esModule: true,
+  default: () => <div data-testid="app">App</div>,
+}));
+
+jest.mock('@/components/utils/ThemeProvider.tsx', () => ({
+  ThemeProvider: ({ children }: { children: React.ReactNode }) => (
+    <div data-testid="theme-provider">{children}</div>
+  ),
+}));
+
+describe('main.tsx', () => {
+  beforeEach(() => {
+    document.body.innerHTML = '<div id="root"></div>';
+  });
+
+  it('has root element available for React app', () => {
+    const rootElement = document.getElementById('root');
+    expect(rootElement).toBeInTheDocument();
+    expect(rootElement).not.toBeNull();
+  });
+
+  it('can create React root without errors', () => {
+    const rootElement = document.getElementById('root');
+    expect(() => {
+      ReactDOM.createRoot(rootElement!);
+    }).not.toThrow();
+  });
+
+  it('imports required React dependencies', () => {
+    expect(React).toBeDefined();
+    expect(ReactDOM).toBeDefined();
+    expect(React.StrictMode).toBeDefined();
+  });
+
+  it('verifies App and ThemeProvider components are available', () => {
+    const App = require('../App.tsx').default;
+    const { ThemeProvider } = require('@/components/utils/ThemeProvider.tsx');
+
+    expect(App).toBeDefined();
+    expect(ThemeProvider).toBeDefined();
+    expect(typeof App).toBe('function');
+    expect(typeof ThemeProvider).toBe('function');
+  });
+});