moy-fp/test/Object/lens.test.js

A functional programming library.

import __ from '../../src/Function/__'
import Identity from '../../src/Functor/Identity/index'
/**
 * (s -> a) -> ((a, s) -> s) -> Lens s a
 * Lens s a = Functor f => (a -> f a) -> s -> f s 
 */
import lens from '../../src/Object/lens'

/**
 * you should not use this similar funciton to get value anywhere in your application
 * if you must need the inner value, you may need Comonad
 * here is just simple for test
 */
const inspect = x => `Identity(${JSON.stringify(x.value)})`

test('lens(not using __), not execute', () => {
  expect(
    lens(a => a.x)((v, a) => a)
  ).toEqual(expect.any(Function))
})

test('lens(not using __), execute', () => {
  expect(
    inspect(lens(a => a.x)((v, a) => a)(Identity)({x: 1}))
  ).toBe('Identity({"x":1})')
})

test('lens(using __), not execute', () => {
  expect(
    lens(__, (v, a) => a)(a => a.x)
  ).toEqual(expect.any(Function))
})