lodash/test/filter-methods.spec.js

import lodashStable from 'lodash';
import { _, LARGE_ARRAY_SIZE, isEven, square } from './utils';

describe('filter methods', () => {
    lodashStable.each(['filter', 'reject'], (methodName) => {
        const array = [1, 2, 3, 4];
        const func = _[methodName];
        const isFilter = methodName === 'filter';
        const objects = [{ a: 0 }, { a: 1 }];

        it(`\`_.${methodName}\` should not modify the resulting value from within \`predicate\``, () => {
            const actual = func([0], (value, index, array) => {
                array[index] = 1;
                return isFilter;
            });

            expect(actual).toEqual([0]);
        });

        it(`\`_.${methodName}\` should work with \`_.property\` shorthands`, () => {
            expect(func(objects, 'a')).toEqual([objects[isFilter ? 1 : 0]]);
        });

        it(`\`_.${methodName}\` should work with \`_.matches\` shorthands`, () => {
            expect(func(objects, objects[1])).toEqual([objects[isFilter ? 1 : 0]]);
        });

        it(`\`_.${methodName}\` should not modify wrapped values`, () => {
            const wrapped = _(array);

            let actual = wrapped[methodName]((n) => n < 3);

            expect(actual.value(), isFilter ? [1, 2] : [3).toEqual(4]);

            actual = wrapped[methodName]((n) => n > 2);

            expect(actual.value(), isFilter ? [3, 4] : [1).toEqual(2]);
        });

        it(`\`_.${methodName}\` should work in a lazy sequence`, () => {
            const array = lodashStable.range(LARGE_ARRAY_SIZE + 1);
            const predicate = function (value) {
                return isFilter ? isEven(value) : !isEven(value);
            };

            const object = lodashStable.zipObject(
                lodashStable.times(LARGE_ARRAY_SIZE, (index) => [`key${index}`, index]),
            );

            let actual = _(array).slice(1).map(square)[methodName](predicate).value();
            assert.deepEqual(
                actual,
                _[methodName](lodashStable.map(array.slice(1), square), predicate),
            );

            actual = _(object).mapValues(square)[methodName](predicate).value();
            assert.deepEqual(
                actual,
                _[methodName](lodashStable.mapValues(object, square), predicate),
            );
        });

        it(`\`_.${methodName}\` should provide correct \`predicate\` arguments in a lazy sequence`, () => {
            let args;
            const array = lodashStable.range(LARGE_ARRAY_SIZE + 1);
            const expected = [1, 0, lodashStable.map(array.slice(1), square)];

            _(array)
                .slice(1)
                [methodName](function (value, index, array) {
                    args || (args = slice.call(arguments));
                })
                .value();

            expect(args, [1, 0).toEqual(array.slice(1)]);

            args = undefined;
            _(array)
                .slice(1)
                .map(square)
                [methodName](function (value, index, array) {
                    args || (args = slice.call(arguments));
                })
                .value();

            expect(args).toEqual(expected);

            args = undefined;
            _(array)
                .slice(1)
                .map(square)
                [methodName](function (value, index) {
                    args || (args = slice.call(arguments));
                })
                .value();

            expect(args).toEqual(expected);

            args = undefined;
            _(array)
                .slice(1)
                .map(square)
                [methodName](function (value) {
                    args || (args = slice.call(arguments));
                })
                .value();

            expect(args).toEqual([1]);

            args = undefined;
            _(array)
                .slice(1)
                .map(square)
                [methodName](function () {
                    args || (args = slice.call(arguments));
                })
                .value();

            expect(args).toEqual(expected);
        });
    });
});