moy-fp/test/Relation/differenceBy.test.js

A functional programming library.

import __ from '../../src/Function/__'
/**
 * (a -> String) -> [a] -> [a] -> [a]
 */
import differenceBy from '../../src/Relation/differenceBy'

test('differenceBy(not using __), first empty array', () => {
  expect(
    differenceBy(x => '' + x.id)([])([{id: 1}, {id: 2}, {id: 3}, {id: 4}])
  ).toEqual([{id: 1}, {id: 2}, {id: 3}, {id: 4}])
})

test('differenceBy(not using __), second empty array', () => {
  expect(
    differenceBy(x => '' + x.id)([{id: 1}, {id: 2}, {id: 3}, {id: 4}])([])
  ).toEqual([])
})

test('differenceBy(not using __), no empty array', () => {
  expect(
    differenceBy(x => '' + x.id)([{id: 1}, {id: 3}])([{id: 1}, {id: 2}, {id: 3}, {id: 4}])
  ).toEqual([{id: 2}, {id: 4}])
})

test('differenceBy(using __), no empty array', () => {
  expect(
    differenceBy(x => '' + x.id, __, [{id: 1}, {id: 2}, {id: 3}, {id: 4}])([{id: 1}, {id: 3}])
  ).toEqual([{id: 2}, {id: 4}])
})