Property Based: Find the best properties

const assert = require('assert'); const fc = require('fast-check'); console.log('fast-check ready...'); // none of those algorithms are supposed to be optimized, they are just implementations examples

const average = (a, b) => (a + b) / 2; 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));

const decompose = (n) => { for (let v = 2 ; v < Math.sqrt(n) ; ++v) if (n % v === 0) return decompose(n/v).concat(v); return [n]; }; fc.assert( fc.property( fc.nat(), n => decompose(n).reduce((acc, cur) => acc*cur, 1) === n));

const removeDuplicates = data => { const noDup = []; for (const c of data) if (noDup.indexOf(c) === -1) noDup.push(c); return noDup; }; fc.assert( fc.property( fc.set(fc.char()), data => assert.deepEqual(removeDuplicates(data), data)));

const contains = (pattern, text) => text.indexOf(pattern) !== -1; fc.assert( fc.property( fc.string(), fc.string(), fc.string(), (a, b, c) => contains(b, a + b + c)));

const binaryContains = (e, data) => { if (data.length === 0) return false; const mid = Math.floor(data.length/2); if (data[mid] === e) return true; return e < data[mid] ? binaryContains(e, data.slice(0, mid)) : binaryContains(e, data.slice(mid+1)); }; const linearContains = (e, data) => data.indexOf(e) !== -1; fc.assert( fc.property( fc.char(), fc.array(fc.char()).map(d => d.sort()), (c, data) => binaryContains(c, data) === linearContains(c, data)));

const pako = require('pako'); const zip = s => pako.deflate(s, { to: 'string' }); const unzip = s => pako.inflate(s, { to: 'string' }); fc.assert( fc.property( fc.string(), v => unzip(zip(v)) === v));

const math = require('mathjs'); fc.assert( fc.property( fc.nat(10000), fc.nat(10000), (a, b) => math.lcm(a, b) * math.gcd(a, b) === a * b));