feat: add simple test file and script

src/test.ts

@@ -0,0 +1,12 @@
+
+import assert from 'assert';
+
+function add(a: number, b: number): number {
+  return a + b;
+}
+
+assert.strictEqual(add(1, 2), 3, 'add(1, 2) should be 3');
+assert.strictEqual(add(0, 0), 0, 'add(0, 0) should be 0');
+assert.strictEqual(add(-1, 1), 0, 'add(-1, 1) should be 0');
+
+console.log('All tests passed!');