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import { reduceBy } from './reduceBy.js'import { prop } from './prop.js'
const byType = prop('type')const sumValues = function (acc, obj){  return acc + obj.val}
const grade = function (score){  return score < 65 ?    'F' :    score < 70 ?      'D' :      score < 80 ?        'C' :        score < 90 ?          'B' :          'A'}
const byGrade = function (student){  return grade(student.score || 0)}
test('splits the list into groups according to the grouping function', () => {  const collectNames = function (acc, student){    return acc.concat(student.name)  }  expect(reduceBy(    collectNames, [], byGrade, getStudents()  )).toEqual({    A : [ 'Dianne', 'Gillian' ],    B : [ 'Abby', 'Chris', 'Irene' ],    C : [ 'Brad', 'Hannah' ],    D : [ 'Fred', 'Jack' ],    F : [ 'Eddy' ],  })})
test('splits the list into mutation-free groups', () => {  const collectNames = function (acc, student){    acc.push(student.name)
    return acc  }  expect(reduceBy(    collectNames, [], byGrade, getStudents()  )).toEqual({    A : [ 'Dianne', 'Gillian' ],    B : [ 'Abby', 'Chris', 'Irene' ],    C : [ 'Brad', 'Hannah' ],    D : [ 'Fred', 'Jack' ],    F : [ 'Eddy' ],  })})
test('returns an empty object if given an empty array', () => {  expect(reduceBy(    sumValues, 0, byType, []  )).toEqual({})})
function getStudents(){  return [    {      name  : 'Abby',      score : 84,    },    {      name  : 'Brad',      score : 73,    },    {      name  : 'Chris',      score : 89,    },    {      name  : 'Dianne',      score : 99,    },    {      name  : 'Eddy',      score : 58,    },    {      name  : 'Fred',      score : 67,    },    {      name  : 'Gillian',      score : 91,    },    {      name  : 'Hannah',      score : 78,    },    {      name  : 'Irene',      score : 85,    },    {      name  : 'Jack',      score : 69,    },  ]}