Generative property testing for Mocha

mocha-testcheck adds the generative testing power of testcheck to Mocha. This allows some of your Mocha 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 mocha-testcheck using npm.

npm install mocha-testcheck

Then include and install mocha-testcheck before your test suite.

require('mocha-testcheck').install();

Example

require('mocha-testcheck').install();
const { expect } = require('chai');

describe('MySpec', () => {

  check.it('accepts an int and a string', gen.int, gen.string, (x, y) => {
    expect(x).to.be.a('number');
    expect(y).to.be.a('string');
  });

});

The gen global object is provided directly by testcheck and defines what type of random values to generate. The test will be run numerous times with different random 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.

Options

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 after the description:

check.it('runs 10 times', {times: 10}, gen.sPosInt, num => {
  assert(x > 0);
});

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

Mocha test interfaces

mocha-testcheck supports all of Mocha's testing interfaces.

BDD

require('mocha-testcheck').install();
const { expect } = require('chai');

describe('MySpec', () => {
  check.it('accepts an int', gen.int, x => {
    expect(x).to.be.a('number');
  });
});

TDD

require('mocha-testcheck').install();
const { expect } = require('chai');

suite('MySpec', () => {
  check.test('accepts an int', gen.int, x => {
    expect(x).to.be.a('number');
  });
});

Exports

require('mocha-testcheck').install();
const { expect } = require('chai');

module.exports = {
  'MySpec': {
    'accepts an int': check(gen.int, x => {
      expect(x).to.be.a('number');
    })
  }
};

Require

This interface is useful if you want to avoid global variables in your tests.

const { describe, it } = require('mocha');
const { check, gen } = require('mocha-testcheck');
const { expect } = require('chai');

describe('MySpec', () => {
  it('accepts an int', check(gen.int, x => {
    expect(x).to.be.a('number');
  });
});