Unchecked

Property based testing made easy!

This library provides a function that you can use for property based testing in any JavaScript testing framework and with any assertion library you like. The idea is that it should be possible to mix property based testing and normal unit-tests using the same tool chain.

This library is build to work together with chance-generators which provides a huge range of composable generators that supports shrinking.

If the generators you supply supports shrinking, then unchecked will try to shrink the error space as much as possible and therefore provide much more precise error cases.

Install

Install it with NPM or add it to your package.json:

$ npm install --save-dev unchecked chance-generators

and require the forall function from unchecked:

const { forall } = require("unchecked");

Usage

Let's imagine we wanted to sort arrays of numbers using this function:

const sort = (arr) => [].concat(arr).sort();

Then we could write a test to ensure the that the resulting array is sorted.

First we need a way to check if the array is sorted:

const isSorted = (array) =>
  array.every((x, i) => array.slice(i).every((y) => x <= y));

Now we are ready to write the tests:

const assert = require("assert");
const util = require("util");
const { array, integer } = require("chance-generators");
 
// generate arrays of integers with length varying from 0 to 30
const numbers = array(integer);
 
forall(array(integer), (numbers) => {
  const sorted = sort(numbers);
 
  assert(isSorted(sorted), `expected ${util.inspect(sorted)} to be sorted`);
});

But that assumption is actually not true as the build-in sort functions is based on converting items to strings and comparing them. So you will get the following error:

Found an error after 1 iteration, 58 additional errors found.
counterexample:
 
  Generated input: [ 10, 2 ]
  with: array({ itemGenerator: integer, min: 0, max: 30 })
 
  expected [ 10, 2 ] to be sorted

If we wanted to fix the problem, we would need to use a comparison function:

const sortNumbers = (arr) => [].concat(arr).sort((a, b) => a - b);

forall(array(integer), (numbers) => {
  const sorted = sortNumbers(numbers);
 
  assert(isSorted(sorted), `expected ${util.inspect(sorted)} to be sorted`);
});

Asynchronous testing

Support for asynchronous testing by returning a promise from the subject function:

const { PassThrough } = require("stream");
const zlib = require("zlib");
const getStream = require("get-stream");
const { string } = require("chance-generators");
 
return forall(string, (text) => {
  const inputStream = new PassThrough();
 
  inputStream.write(text);
  inputStream.end();
 
  const gzip = zlib.createGzip();
  const gunzip = zlib.createGunzip();
 
  inputStream.pipe(gzip).pipe(gunzip);
 
  return getStream(gunzip).then((transformed) => {
    assert.equal(transformed, text);
  });
});

Options

• maxIterations (default 300): the number of iterations that the subject function it ran when no errors occur. You can control the default for this option by setting the environment variable UNCHECKED_MAX_ITERATIONS.
• maxErrorIterations (default 1000): the number of iterations unexpected-check can use to find a better error when an error occurs.
• maxErrors (default 201): the number of found errors before stopping the input shrinking process.

forall(
  array(integer),
  {
    maxIterations: 100,
    maxErrorIterations: 100,
    maxErrors: 10,
  },
  (numbers) => {
    const sorted = sort(numbers);
 
    assert(isSorted(sorted), `expected ${util.inspect(sorted)} to be sorted`);
  }
);

Found an error after 1 iteration, 9 additional errors found.
counterexample:
 
  Generated input: [ 52477443531195, 5636349332, 5783279309 ]
  with: array({ itemGenerator: integer, min: 0, max: 30 })
 
  expected [ 52477443531195, 5636349332, 5783279309 ] to be sorted

As you can see the input shrinking is worse with less iterations, but it will be a bit faster.

Source

The source for this plugin can be found on Github.

MIT License

Copyright (c) 2018 Sune Simonsen sune@we-knowhow.dk

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.