updated design

packages/diff-engine/vitest.config.ts

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    include: ['__tests__/**/*.test.ts'],
+    coverage: {
+      provider: 'v8',
+      include: ['src/**/*.ts'],
+      exclude: ['src/index.ts'],
+      thresholds: { lines: 85, functions: 85, branches: 80 },
+    },
+  },
+});