js-practice/test/array/letter-combinations-of-a-phone-number.test.js

import letterCombinations from '../../src/array/letter-combinations-of-a-phone-number'

test('letterCombinations', () => {
  expect(letterCombinations('23')).toEqual(['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf'])
})