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import { add } from './add.js'import { concat } from './concat.js'import { reduce, reduceStopper } from './reduce.js'
const reducer = (  prev, current, i) => {  expect(i).toBeNumber()
  return prev + current}const initialValue = 1const list = [ 1, 2, 3 ]const ERROR = 'reduce: list must be array or iterable'
test('happy', () => {  expect(reduce(    reducer, initialValue, list  )).toBe(7)})
test('with object as iterable', () => {  expect(() =>    reduce(      reducer, initialValue, {        a : 1,        b : 2,      }    )).toThrowWithMessage(TypeError, ERROR)})
test('with undefined as iterable', () => {  expect(() => reduce(    reducer, 0, {}  )).toThrowWithMessage(TypeError, ERROR)})
test('with reduceStopper', () => {  let maxIndex  const reducer = (    prev, current, i  ) => {    maxIndex = i
    return current === 2 ? reduceStopper(current) : prev  }  expect(reduce(    reducer, initialValue, list  )).toBe(2)  expect(maxIndex).toBe(1)})
test('returns the accumulator for a null list', () => {  expect(reduce(    add, 0, null  )).toBe(0)  expect(reduce(    concat, [], null  )).toEqual([])})
test('returns the accumulator for an undefined list', () => {  expect(reduce(    add, 0, undefined  )).toBe(0)  expect(reduce(    concat, [], undefined  )).toEqual([])})