import prepend from '../../utils/prepend'; describe('prepend', () => { it('should prepend value to an array', () => { expect(prepend([2, 3, 4], 1)).toEqual([1, 2, 3, 4]); expect( prepend( [ { firstName: '2', lastName: 'Luo', id: '75309979-e340-49eb-8016-5f67bfb56c1c', }, { firstName: '3', lastName: 'Luo', id: '75309979-e340-49eb-8016-5f67bfb56c1c', }, { firstName: '4', lastName: 'Luo', id: '75309979-e340-49eb-8016-5f67bfb56c1c', }, ], { firstName: '1', lastName: 'Luo', id: '75309979-e340-49eb-8016-5f67bfb56c1c', }, ), ).toEqual([ { firstName: '1', lastName: 'Luo', id: '75309979-e340-49eb-8016-5f67bfb56c1c', }, { firstName: '2', lastName: 'Luo', id: '75309979-e340-49eb-8016-5f67bfb56c1c', }, { firstName: '3', lastName: 'Luo', id: '75309979-e340-49eb-8016-5f67bfb56c1c', }, { firstName: '4', lastName: 'Luo', id: '75309979-e340-49eb-8016-5f67bfb56c1c', }, ]); }); it('should prepend undefined as value when value to be prepended is falsy', () => { expect(prepend([2, 3, 4], 0)).toEqual([0, 2, 3, 4]); expect(prepend([2, 3, 4] as (number | boolean)[], false)).toEqual([ false, 2, 3, 4, ]); expect(prepend([2, 3, 4] as (number | string)[], '')).toEqual([ '', 2, 3, 4, ]); expect(prepend([2, 3, 4], undefined)).toEqual([undefined, 2, 3, 4]); }); it('should spread value when it is an array at one deep-level', () => { expect(prepend([3, 4], [1, 2])).toEqual([1, 2, 3, 4]); expect(prepend([3, 4], [[1], 2])).toEqual([[1], 2, 3, 4]); }); });