text: var lens = require('.')
  
  var obj = {
    a: 2,
    b: 3
  }
  
  var lens = lens(obj => obj.a, (b, obj) => ({ ...obj, b }))
  
  test('returns value by getter', () => {
    expect(lens(obj).get()).toBe(2)
  })
  
  test('changes value by setter', () => {
    expect(lens(obj).set(2)).toEqual({ a: 2, b: 2 })
  })
  
  test("doesn't mutate real object", () => {
    lens(obj).set(2)
    expect(obj).toEqual({ a: 2, b: 3 })
  })
  