dubzzz

const contains = (pattern, text) => {
  return text.substr(1).indexOf(pattern) !== -1;
};

dubzzz

fc.sample(
  fc.property(
    fc.string(), fc.string(), fc.string(),
    (a, b, c) => contains(b, a+b+c))
);

dubzzz

const fc = require('fast-check');

fc.assert(
  fc.property(
    fc.string(), fc.string(), fc.string(),
    (a, b, c) => contains(b, a+b+c))
);

dubzzz

'\u{1f431}'           // result: '🐱'
'\u{1f431}'.length    // result: 2
'\u{1f431}'.split('') // result: ['\ud83d', '\udc31']
encodeURIComponent('\u{1f431}')           // result: '%F0%9F%90%B1'
encodeURIComponent('\u{1f431}'.charAt(0)) // error: URIError: malformed URI sequence

dubzzz

fc.assert(
  fc.property(
    fc.nat(),
    n => decompose(n).reduce((acc, cur) => acc*cur, 1) === n));

dubzzz

fc.assert(
  fc.property(
    fc.string(), fc.string(), fc.string(),
    (a, b, c) => contains(b, a + b + c)));

dubzzz

fc.assert(
  fc.property(
    fc.char(), fc.array(fc.char()).map(d => d.sort()),
    (c, data) => binaryContains(c, data) === linearContains(c, data)));

dubzzz

fc.assert(
  fc.property(
    fc.string(),
    v => unzip(zip(v)) === v));

dubzzz

fc.assert(
  fc.property(
    fc.nat(), fc.nat(),
    (a, b) => lcm(a, b) * gcd(a, b) === a * b));

dubzzz

fc.assert(
  fc.property(
    fc.integer(), fc.integer(),
    (a, b) => a <= b
      ? a <= average(a, b) && average(a, b) <= b
      : b <= average(a, b) && average(a, b) <= a));