How to use

anything

function

in

fast-check

test('isEmpty vs nonEmpty', () => {
 fc.assert(
  fc.property(fc.anything(), value => {
   const option = Option.of(value)

   return option.isEmpty() !== option.nonEmpty()
  }),
 )
})

describe('inheritance', () => {
 test('instance of Option', () => {
  fc.assert(
   fc.property(fc.anything(), value => Option.of(value) instanceof Option),
  )
 })

 test('instance of None or Some', () => {
  fc.assert(
   fc.property(fc.anything(), value => {
    const isSome = Option.of(value) instanceof Some
    const isNone = Option.of(value) instanceof None

    return isSome || isNone
   }),
  )
 })
})

describe('nonEmpty values', () => {
 test('Option must be non-empty', () => {
  fc.assert(fc.property(nonEmpty(), value => Option.of(value).nonEmpty()))
 })

 test('Option must have a same value', () => {
  fc.assert(
   fc.property(nonEmpty(), value => Option.of(value).get() === value),
  )
 })

 test('Option must skip getOrElse', () => {
  fc.assert(
   fc.property(
    nonEmpty(),
    fc.anything(),
    (value, or) => Option.of(value).getOrElse(or) === value,
   ),
  )
 })
})