Utility library that provides useful functionality for writing tests

Usage no npm install needed!

<script type="module">
  import vamshipTestUtils from 'https://cdn.skypack.dev/@vamship/test-utils';



Utility library that provides useful functionality for writing tests

This library exports a collection of classes and modules that makes writing tests easier. While not specific to any given testing library or framework, this library has been developed with mocha and chai in mind.

API Documentation

API documentation can be found here.


Testing is an important part of application development, and as well tested applications and libraries grow in size, so do the automated tests that go with them. Over time, common test patterns emerge, and one finds oneself rewriting the same scaffolding or utility classes to execute these test patterns.

The idea behind this library is to encapsulate these testing patterns, or at least the building blocks for these patterns into a single library that can be imported and reused in other projects.

For example, the testValues module exports a collection of functions that can be used to generate dummy values for testing. The ObjectMock class provides a simple way to mock out methods on objects allowing unit tests to be executed while having mocks replace dependencies for the entities under test. The SuperSpyBuilder class can be used to apply spy methods on inherited methods, including the super() constructor call. This enables the creation of tests that treat parent classes as black boxes.


This library can be installed using npm:

npm install @vamship/test-utils


The classes and modules exported by this library are independent, and can be used by importing them into the source code as follows:

const _rewire = require('rewire');
const _testValues = require('@vamship/test-utils').testValues;
const {ArgError} = require('@vamship/arg-utils').args;

let User = require('../../src/user');

describe('MyClass', () => {
    beforeEach(() => {
        // Load up the object under test. Use rewire to load the object
        // so that mocks can be assigned if necessary.
        User = _rewire('../../src/user');

    it('should throw an error if invoked without a valid username', () => {
        const error = 'Invalid username specified (arg #1)';

        // Create an array of test values containing all types except a string,
        // and then add an empty string to that list
        const inputs = _testValues.allButString('');

        inputs.forEach((username) => {
            const wrapper = () => {
                return new User(username);

            expect(wrapper).to.throw(ArgError, error);

The example above is just one of many possible examples of how this library and its exported modules and classes may be used. For more information, please review the API documentation.