moy-fp/test/Functor/Maybe/index.test.js

A functional programming library.

import Maybe from '../../../src/Functor/Maybe/index'

/**
 * 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 => x.value === null || x.value === undefined ? 
                      'Nothing' :
                      `Just(${x.value})`

describe('test Maybe', () => {
  test('Just', () => {
    expect(
      inspect(Maybe(12))
    ).toBe('Just(12)')
  })

  test('Nothing', () => {
    expect(
      inspect(Maybe(null))
    ).toBe('Nothing')
  })
})

describe('test of', () => {
  test('Just', () => {
    expect(
      inspect(Maybe.of(12))
    ).toBe('Just(12)')
  })

  test('Nothing', () => {
    expect(
      inspect(Maybe.of(null))
    ).toBe('Nothing')
  })
})

describe('test map', () => {
  test('Just', () => {
    expect(
      inspect(Maybe.of(12).map(x => x + 1))
    ).toBe('Just(13)')
  })

  test('Nothing', () => {
    expect(
      inspect(Maybe.of(null).map(x => x + 1))
    ).toBe('Nothing')
  })
})

describe('test join', () => {
  test('Just', () => {
    expect(
      inspect(Maybe.of(
        Maybe.of(12)
      ).join())
    ).toBe('Just(12)')
  })

  test('Nothing', () => {
    expect(
      inspect(Maybe.of(null).join())
    ).toBe('Nothing')
  })
})

describe('test chain', () => {
  test('Just', () => {
    expect(
      inspect(Maybe.of(12).chain(
        x => Maybe.of(x + 1)
      ))
    ).toBe('Just(13)')
  })

  test('Nothing', () => {
    expect(
      inspect(Maybe.of(null).chain(
        x => Maybe.of(x + 1)
      ))
    ).toBe('Nothing')
  })
})

describe('test ap', () => {
  test('Just', () => {
    expect(
      inspect(Maybe.of(x => x + 1).ap(
        Maybe.of(12)
      ))
    ).toBe('Just(13)')
  })

  test('Nothing', () => {
    expect(
      inspect(Maybe.of(null).ap(
        Maybe.of(12)
      ))
    ).toBe('Nothing')
  })
})

test('test Object.prototype.toString.call',() => {
  expect(
    Object.prototype.toString.call(
      Maybe.of(12)
    )
  ).toBe('[object Maybe]')
})