Verify edge cases and input validation for tracking fallback

utils/tracking.empty-fallback.test.ts

@@ -0,0 +1,96 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { trackUser } from './tracking';
+
+describe('trackUser Edge Cases & Empty Fallback Tests', () => {
+  let originalWindow: typeof globalThis.window;
+  let originalNavigator: typeof globalThis.navigator;
+  let originalFetch: typeof globalThis.fetch;
+  let originalBlob: typeof globalThis.Blob;
+
+  beforeEach(() => {
+    originalWindow = globalThis.window;
+    originalNavigator = globalThis.navigator;
+    originalFetch = globalThis.fetch;
+    originalBlob = globalThis.Blob;
+
+    globalThis.window = {} as unknown as typeof globalThis.window;
+    globalThis.navigator = {
+      sendBeacon: vi.fn().mockReturnValue(true),
+    } as unknown as typeof globalThis.navigator;
+    globalThis.fetch = vi.fn().mockResolvedValue({ ok: true });
+
+    // Ensure Blob is polyfilled securely to prevent hydration or runtime errors in CI
+    if (typeof globalThis.Blob === 'undefined') {
+      globalThis.Blob = class Blob {
+        constructor(
+          public parts: string[],
+          public options: Record<string, string>
+        ) {}
+      } as unknown as typeof globalThis.Blob;
+    }
+
+    vi.spyOn(console, 'error').mockImplementation(() => undefined);
+  });
+
+  afterEach(() => {
+    globalThis.window = originalWindow;
+    globalThis.navigator = originalNavigator;
+    globalThis.fetch = originalFetch;
+    globalThis.Blob = originalBlob;
+    vi.restoreAllMocks();
+  });
+
+  it('1. correctly short-circuits and ignores empty string usernames without throwing', () => {
+    trackUser('');
+    expect(globalThis.navigator.sendBeacon).not.toHaveBeenCalled();
+    expect(globalThis.fetch).not.toHaveBeenCalled();
+  });
+
+  it('2. safely acts as a non-breaking no-op when executing in a headless/server environment (missing window/navigator)', () => {
+    // Simulate empty server environment without triggering TypeScript readonly errors
+    const globals = globalThis as unknown as Record<string, unknown>;
+    delete globals.window;
+    delete globals.navigator;
+
+    expect(() => trackUser('octocat')).not.toThrow();
+  });
+
+  it('3. seamlessly falls back to the fetch API when navigator.sendBeacon is unavailable or undefined', () => {
+    const nav = globalThis.navigator as unknown as Record<string, unknown>;
+    delete nav.sendBeacon;
+
+    trackUser('octocat');
+    expect(globalThis.fetch).toHaveBeenCalledWith(
+      '/api/track-user',
+      expect.objectContaining({
+        method: 'POST',
+        keepalive: true,
+      })
+    );
+  });
+
+  it('4. gracefully tolerates beacon queuing failures by automatically deploying the fetch fallback', () => {
+    // sendBeacon returns false when the queue is full or payload is too large
+    globalThis.navigator = {
+      sendBeacon: vi.fn().mockReturnValue(false),
+    } as unknown as typeof globalThis.navigator;
+
+    trackUser('octocat');
+    expect(globalThis.navigator.sendBeacon).toHaveBeenCalled();
+    expect(globalThis.fetch).toHaveBeenCalled(); // Triggered fallback
+  });
+
+  it('5. guarantees no unhandled promise rejections if the fallback fetch network request completely fails', async () => {
+    globalThis.navigator = {
+      sendBeacon: vi.fn().mockReturnValue(false),
+    } as unknown as typeof globalThis.navigator;
+    globalThis.fetch = vi.fn().mockRejectedValue(new Error('Network offline'));
+
+    // Should not throw or cause unhandled rejections
+    expect(() => trackUser('octocat')).not.toThrow();
+
+    // Wait a tick to ensure async catch block executes cleanly
+    await new Promise(process.nextTick);
+    expect(console.error).toHaveBeenCalled();
+  });
+});