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import { chain } from './chain'
const duplicate = n => [ n, n ]
test('happy', () => {  const fn = x => [ x * 2 ]  const list = [ 1, 2, 3 ]
  const result = chain(fn, list)
  expect(result).toEqual([ 2, 4, 6 ])})
test('maps then flattens one level', () => {  expect(chain(duplicate, [ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])})
test('maps then flattens one level - curry', () => {  expect(chain(duplicate)([ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])})
test('flattens only one level', () => {  const nest = n => [ [ n ] ]  expect(chain(nest, [ 1, 2, 3 ])).toEqual([ [ 1 ], [ 2 ], [ 3 ] ])})