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checkers

npm version Build Status

Property-based testing for JavaScript via ClojureScript's test.check.

test.check is a Clojure property-based testing tool inspired by QuickCheck. The core idea of test.check is that instead of enumerating expected input and output for unit tests, you write properties about your function that should hold true for all inputs. This lets you write concise, powerful tests.

Checkers brings the power of test.check to plain ol' JavaScript.

Install

npm install checkers --save

Usage

var checkers = require('checkers');
var gen = checkers.gen;

// Property is incorrect
checkers.forAll(
    [gen.int],
    function(i) {
        return i * i > i;
    }
).check(1000);

// Property is now correct
checkers.forAll(
    [gen.int],
    function(i) {
        return i * i >= i;
    }
).check(1000);

// Check property with a particular seed
checkers.forAll(
    [gen.int],
    function(i) {
        return i * i >= i;
    }
).check(1000, {seed: 1422111938215});

Usage with Mocha

Checkers comes with a helper function to make writing tests for mocha simpler.

var checking = require('checkers/mocha');
var gen = checking.gen;
describe("Addition", function() {
    checking("+1", [gen.int], function(i) {
        return i + 1 > i;
    }, 100, {seed: 1422111938215});
});

The count is optional, and defaults to 1000. The extra options are also optional.

Full Documentation

More coming soon!

For now you'll have to rely on the examples in the test folder.

Building your own generators

The simplest way to build your own generators is with gen.fmap. This lets you apply a function to generated values to produce new ones.

Here's an example of generating instances of a 3-D Point object.

var genPoint = gen.fmap(
    function(p) { return new Point(p.x, p.y, p.z) },
    gen.object({ x: gen.int, y: gen.int, z: gen.int })
);

Testing the generator in a Node REPL is also simple.

$ # assumes you've already done npm install --save-dev checkers
$ node
>
> var checkers = require('checkers');
undefined
>
> var gen = checkers.gen;
undefined
>
> var newlog = (x,y,z) => console.log(`new point ${x} ${y} ${z}`);
undefined
>
> var Point = function(x,y,z) { newlog(x,y,z); this.coord=[x,y,z]; return this; }
undefined
>
> var genPoint = gen.fmap( p => new Point(p.x, p.y, p.z) , gen.object({ x: gen.int, y: gen.int, z: gen.int }) );
undefined
>
> checkers.sample(genPoint);
new point 0 0 0
new point -1 -1 -1
new point -1 -1 2
new point 3 -2 -2
new point 1 -2 2
new point 0 -4 0
new point -4 1 -3
new point -4 -1 -6
new point 3 -2 -1
new point 4 2 -6
[ { coord: [ 0, 0, 0 ] },
  { coord: [ -1, -1, -1 ] },
  { coord: [ -1, -1, 2 ] },
  { coord: [ 3, -2, -2 ] },
  { coord: [ 1, -2, 2 ] },
  { coord: [ 0, -4, 0 ] },
  { coord: [ -4, 1, -3 ] },
  { coord: [ -4, -1, -6 ] },
  { coord: [ 3, -2, -1 ] },
  { coord: [ 4, 2, -6 ] } ]

TODO

  • Generator tests
  • Generator docs
  • Sugar for other testing frameworks?
  • Tutorial
  • Better examples

Development

See npm run or package.json for a list of available scripts.

You will need leiningen in order to build locally.

License

Distributed under the Eclipse Public License.

checkers is Copyright © 2015 Glen Mailer and contributors.

test.check is Copyright Rich Hickey, Reid Draper and contributors.