lodash/test/countBy.spec.ts

import assert from 'node:assert';
import lodashStable from 'lodash';
import { LARGE_ARRAY_SIZE } from './utils';
import countBy from '../src/countBy';

describe('countBy', () => {
    const array = [6.1, 4.2, 6.3];

    it('should transform keys by `iteratee`', () => {
        const actual = countBy(array, Math.floor);
        assert.deepStrictEqual(actual, { '4': 1, '6': 2 });
    });

    it('should use `_.identity` when `iteratee` is nullish', () => {
        const array = [4, 6, 6],
            values = [, null, undefined],
            expected = lodashStable.map(values, lodashStable.constant({ '4': 1, '6': 2 }));

        const actual = lodashStable.map(values, (value, index) =>
            index ? countBy(array, value) : countBy(array),
        );

        assert.deepStrictEqual(actual, expected);
    });

    it('should work with `_.property` shorthands', () => {
        const actual = countBy(['one', 'two', 'three'], 'length');
        assert.deepStrictEqual(actual, { '3': 2, '5': 1 });
    });

    it('should only add values to own, not inherited, properties', () => {
        const actual = countBy(array, (n) =>
            Math.floor(n) > 4 ? 'hasOwnProperty' : 'constructor',
        );

        assert.deepStrictEqual(actual.constructor, 1);
        assert.deepStrictEqual(actual.hasOwnProperty, 2);
    });

    it('should work with a number for `iteratee`', () => {
        const array = [
            [1, 'a'],
            [2, 'a'],
            [2, 'b'],
        ];

        assert.deepStrictEqual(countBy(array, 0), { '1': 1, '2': 2 });
        assert.deepStrictEqual(countBy(array, 1), { a: 2, b: 1 });
    });

    it('should work with an object for `collection`', () => {
        const actual = countBy({ a: 6.1, b: 4.2, c: 6.3 }, Math.floor);
        assert.deepStrictEqual(actual, { '4': 1, '6': 2 });
    });

    it('should work in a lazy sequence', () => {
        const array = lodashStable
            .range(LARGE_ARRAY_SIZE)
            .concat(
                lodashStable.range(Math.floor(LARGE_ARRAY_SIZE / 2), LARGE_ARRAY_SIZE),
                lodashStable.range(Math.floor(LARGE_ARRAY_SIZE / 1.5), LARGE_ARRAY_SIZE),
            );

        const actual = _(array).countBy().map(square).filter(isEven).take().value();

        assert.deepEqual(actual, _.take(_.filter(_.map(countBy(array), square), isEven)));
    });
});