alvarocastro/pick-random-weighted

import test from 'ava';
import { pick, Picker } from './index.js';

// Mock random number generation.
const randomGen = function (sequence = []) {
    return function () {
        const n = sequence.shift();
        sequence.push(n);
        return n;
    };
};

test('Should return ’undefined’ with empty lists', t => {
    t.assert(pick([]) === undefined);
});

test('Should work with lists of one item', t => {
    const picker = new Picker(randomGen([0.1, 0.6, 0.3, 0.4]));
    const data = [
        ['a', 1],
    ];

    t.assert(picker.pick(data) === 'a');
    t.assert(picker.pick(data) !== 'b');
});

test('Should work with lists of multiple items', t => {
    const picker = new Picker(randomGen([0.1, 0.6, 0.3, 0.4]));
    const data = [
        ['a', 2],
        ['b', 2],
        ['c', 4],
        ['d', 3],
    ];

    t.is(picker.pick(data), 'a');
    t.is(picker.pick(data), 'c');
    t.is(picker.pick(data), 'b');
    t.is(picker.pick(data), 'c');
});

test('Should validate input', t => {
    t.throws(() => pick(), {
        instanceOf: TypeError,
        message: 'Expected an Array as the first argument',
    });
    t.throws(() => pick('bad'), {
        instanceOf: TypeError,
        message: 'Expected an Array as the first argument',
    });
});