day9.ts

import fc from "fast-check";
import isProbablyEnchantedWord from "./advent-day-09.mjs";
import { test, expect } from "bun:test";

const char = fc.stringMatching(/^\w$/);
const word = fc.stringMatching(/^\w+$/);

const palindrome = fc.oneof(
  char,
  fc
    .tuple(word, fc.string({ maxLength: 1 }))
    .map(([word, sep]) => word + sep + word.split("").reverse().join(""))
    .filter((w) => !w.includes("\n"))
);

// declare isProbablyEnchantedWord(word: string): boolean;
test("day 9: false negatives", () => {
  fc.assert(
    fc.property(palindrome, (word) => {
      expect(isProbablyEnchantedWord(word)).toEqual(true);
    })
  );
});

test("day 9: false positives", () => {
  fc.assert(
    fc.property(
      word,
      word,

      (word1, word2) => {
        fc.pre(word1.length >= 1);
        fc.pre(!word1.includes(word2));
        expect(isProbablyEnchantedWord(word2 + word1)).toEqual(false);
        expect(isProbablyEnchantedWord(word1 + word2)).toEqual(false);
      }
    )
  );
});

Counter example, a false positive:

ba