🧪 Add Vitest testing framework with basic composition test

Set up testing infrastructure using Vitest and React Testing Library.
Add test verifying empty MyComposition renders without errors.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

videos/src/Composition.test.tsx

@@ -0,0 +1,15 @@
+import { describe, it, expect } from "vitest";
+import { render } from "@testing-library/react";
+import { MyComposition } from "./Composition";
+
+describe("MyComposition", () => {
+  it("renders without errors", () => {
+    const { container } = render(<MyComposition />);
+    expect(container).toBeInTheDocument();
+  });
+
+  it("returns null (empty composition)", () => {
+    const { container } = render(<MyComposition />);
+    expect(container.firstChild).toBeNull();
+  });
+});

videos/src/test/setup.ts

@@ -0,0 +1 @@
+import "@testing-library/jest-dom/vitest";