lodash/test/isUndefined.spec.ts

import assert from 'node:assert';
import lodashStable from 'lodash';
import { falsey, args, slice, symbol, realm } from './utils';
import isUndefined from '../src/isUndefined';

describe('isUndefined', () => {
    it('should return `true` for `undefined` values', () => {
        assert.strictEqual(isUndefined(), true);
        assert.strictEqual(isUndefined(undefined), true);
    });

    it('should return `false` for non `undefined` values', () => {
        const expected = lodashStable.map(falsey, (value) => value === undefined);

        const actual = lodashStable.map(falsey, (value, index) =>
            index ? isUndefined(value) : isUndefined(),
        );

        assert.deepStrictEqual(actual, expected);

        assert.strictEqual(isUndefined(args), false);
        assert.strictEqual(isUndefined([1, 2, 3]), false);
        assert.strictEqual(isUndefined(true), false);
        assert.strictEqual(isUndefined(new Date()), false);
        assert.strictEqual(isUndefined(new Error()), false);
        assert.strictEqual(isUndefined(slice), false);
        assert.strictEqual(isUndefined({ a: 1 }), false);
        assert.strictEqual(isUndefined(1), false);
        assert.strictEqual(isUndefined(/x/), false);
        assert.strictEqual(isUndefined('a'), false);

        if (Symbol) {
            assert.strictEqual(isUndefined(symbol), false);
        }
    });

    it('should work with `undefined` from another realm', () => {
        if (realm.object) {
            assert.strictEqual(isUndefined(realm.undefined), true);
        }
    });
});