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1.0.0-rc.0 • Public • Published

Generative property testing for AVA

ava-check adds the generative testing power of testcheck-js to AVA. This allows some of your AVA tests to accept arguments and ensure your tests pass not just under your contrived test cases but also pass for hundreds of randomly generated test cases.

Getting started

Install ava-check using yarn.

yarn add --dev ava-check

Or using npm

npm install --save-dev ava-check

Then include ava-check in your test.

const { check, gen } = require('ava-check')


const test = require('ava')
const { check, gen } = require('ava-check')
test('addition is commutative', check(gen.int, gen.int, (t, numA, numB) => {
  t.true(numA + numB === numB + numA)

The gen object is provided directly by testcheck and defines what type of values to generate. The test will be run numerous times with randomly generated values, ensuring all expectations are met for every run. If a test expectation fails, then the test will re-run with "smaller" values until the smallest failing value is found which can better help explain edge cases with your test and produce consistent results, despite being initially fueled by randomness.

For example, here's a test which we expect would fail:

const test = require('ava')
const { check, gen } = require('ava-check')
test('division is commutative', check(gen.sPosInt, gen.sPosInt, (t, numA, numB) => {
  t.true(numA / numB === numB / numA)

When we run this test, we find the smallest failing test:

> ava test
  1 failed
  division is commutative ( 1, 2 )
  t.true(numA / numB === numB / numA)
         |      |        |      |
         1      2        2      1


If a test is taking a long time, needs to generate larger values, or should be run with a consistent random seed, you can alter the behavior with options:

  times: number;   // the number of test cases to run. Default: 100
  maxSize: number; // the maximum "size" of the test data. Default: 200
  seed: number;    // defaults to a random value from 1 to 2^32-1.

To use these options with your check, include an options object before the argument generators.

test('runs 10 times', check({ times: 10 }, gen.posInt, (t, n) => {
  t.true(>= 0)

To learn more about property testing, or to learn about the available value generators, check out testcheck.

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