chore: import upstream snapshot with attribution

tools/challenge-helper-scripts/helpers/utils.test.ts

@@ -0,0 +1,37 @@
+import { describe, it, expect } from 'vitest';
+import { insertInto } from './utils.js';
+
+describe('insertInto', () => {
+  it('should not modify the original array', () => {
+    const arr = [1, 2, 3];
+    const result = insertInto(arr, 1, 99);
+    expect(arr).toEqual([1, 2, 3]);
+    expect(result).not.toBe(arr);
+  });
+
+  it('should insert at the end if the index is larger than the original array', () => {
+    const arr = [1, 2, 3];
+    const result = insertInto(arr, 10, 99);
+    expect(result).toEqual([1, 2, 3, 99]);
+  });
+
+  it('should insert at the beginning if the index is <= 0', () => {
+    const arr = [1, 2, 3];
+    const result = insertInto(arr, 0, 99);
+    expect(result).toEqual([99, 1, 2, 3]);
+    const resultNeg = insertInto(arr, -5, 99);
+    expect(resultNeg).toEqual([99, 1, 2, 3]);
+  });
+
+  it('should insert at the correct index', () => {
+    const arr = [1, 2, 3];
+    const result = insertInto(arr, 1, 99);
+    expect(result).toEqual([1, 99, 2, 3]);
+  });
+
+  it('should work with empty arrays', () => {
+    const arr: number[] = [];
+    const result = insertInto(arr, 0, 99);
+    expect(result).toEqual([99]);
+  });
+});