Property-based testing for TypeScript and JavaScript

This is an implementation of property-based testing a'la QuickCheck for TypeScript. It works with plain JavaScript and languages like CoffeeScript too.

Shrinking is done by generating lazy rose trees of values directly. This means that you can map and chain generators and get correct shrinking functions "for free". This is a deviation from the original Haskell library but works well in languages without typeclasses. (The same approach is taken in other implementations such as Hedgehog for Haskell, Hypothesis for Python and test.check for Clojure)

Usage with mocha and jest

import * as QC from 'proptest'
const property = QC.createProperty(it)
 
describe('f', () => {
  property(
    'is commutative',
    QC.nat.two(),
    ([x, y]) => (expect(f(x, y)).toEqual(f(y, x)), true)
  )
})

(to be improved; remove returning a boolean: discussion)

Usage with tape

import * as QC from 'proptest'
const check = QC.adaptTape(test)
 
check('f commutative', QC.nat.two(), ([x, y]) => f(x, y) === f(y, x))

Usage with AVA

import * as QC from 'proptest'
test('f commutative', t => {
  t.true(QC.stdoutForall(QC.nat.two(), ([x, y]) => f(x, y) === f(y, x)))
})

(to be improved, also see ava#1692)

Usage without a library as an assertion

import * as QC from 'proptest'
QC.assertForall(QC.nat.two(), ([x, y]) => f(x, y) === f(y, x))

The API exports a function search which return returns {'ok': true} if the property passed or {'ok': false} and the counterexample (or other information) if it did not.

Installation

You can grab it from npm:

npm i -D proptest

You may use yarn:

yarn add --dev proptest

Contributors

• Simon Friis Vindum @paldepind (commits)

Ongoing discussions

• Should properties return a boolean of success or just not throw an assertion? #6 #5

License

MIT