Added API tests + added vitest.config.ts + added fallback of window.fetch with xmlhttprequest

src/test/api.test.tsx

@@ -0,0 +1,18 @@
+import { describe, test, expect } from 'vitest';
+import { fetchConfiguration } from '../App';
+
+describe('API test', () => {
+  test('Load environment', () => {
+    const url = import.meta.env.VITE_API_URL;
+    expect(url).toBe('http://localhost:5000');
+  });
+
+  test('Fetch configuration', async() => {
+    const configuration = await fetchConfiguration();
+    expect(configuration.MainContainer).toBeDefined();
+    expect(configuration.MainContainer.Height).toBeGreaterThan(0);
+    expect(configuration.MainContainer.Width).toBeGreaterThan(0);
+    expect(configuration.AvailableContainers.length).toBeGreaterThan(-1);
+    expect(configuration.AvailableSymbols.length).toBeGreaterThan(-1);
+  });
+});