import {
  pairOf,
  positiveInt,
  property,
  shrinkPair,
  shrinkPositive,
} from './property';

// from https://github.com/jlink/shrinking-challenge/blob/main/challenges/difference.md
const predicate1: (pair: [number, number]) => boolean = ([x, y]) =>
  x < 10 || x !== y;

describe('Find minimal counterexample', () => {
  test('do not shrink example if no shrinker given', () => {
    const result = property(pairOf(positiveInt), predicate1)(42, 1);
    expect(result.result).toBe('Falsified');
    expect(result.counterexample).toBeNull;
  });

  test('shrink example if shrinker given', () => {
    const result = property(
      pairOf(positiveInt),
      predicate1,
      shrinkPair(shrinkPositive, shrinkPositive),
    )(42, 1);
    expect(result.result).toBe('Falsified');
    if (result.counterexample !== null) {
      expect(result.counterexample.counterexample).toStrictEqual([10, 10]);
    } else {
      fail('no counterexample');
    }
  });
});