text: import { countBy } from './countBy.js'
  
  const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]
  
  test('happy', () => {
    const result = countBy(x => x.toLowerCase(), list)
    expect(result).toEqual({
      a : 2,
      b : 2,
      c : 2,
    })
  })
  