Function collisionKeys

__tests__/Map.collision.ts:11–22

* Generates `2 ** rounds` distinct strings that all share the same * `Immutable.hash()`, by concatenating the classic "Aa"/"BB" collision blocks * (both equal `65 * 31 + 97 === 66 * 31 + 66 === 2112` under the JVM-style * `31 * h + c` string hash). Inserting these into a Map forces them all into

(rounds: number)

 * single HashCollisionNode — the hash-flooding scenario this code guards.
 */
function collisionKeys(rounds: number): Array<string> {
  let keys = [''];
  for (let i = 0; i < rounds; i++) {
    const next: Array<string> = [];
    for (const k of keys) {
      next.push(k + 'Aa');
      next.push(k + 'BB');
    }
    keys = next;
  }
  return keys;
}

describe('Map hash collisions', () => {
  it('the generated keys really do collide (test is meaningful)', () => {