Testing · Code with Hugo

How to run Jest tests sequentially

By default Jest runs tests in parallel with a “a worker pool of child processes that run tests” (Jest CLI docs). As per the Jest documentation, running tests in sequence (serially), can be helpful for debugging purposes and for test run performance reasons. ...

#javascript #jest #node #es6 #testing

Jest Full and Partial Mock/Spy of CommonJS and ES6 Module Imports

JavaScript import/require module testing do’s and don’ts with Jest The example repository is available at github.com/HugoDF/mock-spy-module-import. This post goes through how to achieve different types of module mocking scenarios with Jest. From simple Import interc ...

#javascript #jest #testing #node

Jest ignore or exclude file/function/statement from test coverage

In computer science, test coverage is a measure used to describe the degree to which the source code of a program is executed when a particular test suite runs. Code coverage - Wikipedia Code coverage is usually used as a quality metric for software eg. “Our code has to have 80 ...

#JavaScript #jest #Node #Testing #date

Mocking/stubbing the current Date in Jest tests

There are situations where new Date() or Date.now is used in application code. That code needs to be tested, and it’s always a struggle to remember how to mock/stub or spy on Date.now/new Date with Jest. This post goes through multiple approaches to mocking, stubbing and spying o ...

#javascript #node #jest #testing #MongoDB

Avoiding recursion pitfalls: MongoDB nested query clause addition and removal

A case-study on where recursion can be useful for enterprise Node.js applications and how to avoid its common pitfalls like RangeError: Maximum call stack size exceeded. The full repository for this post is on GitHub: github.com/HugoDF/mongo-query-clause-modification We’ll ...

#testing #jest #node #javascript #jest

Jest assert over single or specific argument/parameters with .toHaveBeenCalledWith and expect.anything()

With Jest it’s possible to assert of single or specific arguments/parameters of a mock function call with .toHaveBeenCalled/.toBeCalled and expect.anything(). The full example repository is at github.com/HugoDF/jest-specific-argument-assert, more specifically lines 17-66 ...

#Node #jest #Testing #JavaScript

JavaScript Object.defineProperty for a function: create mock object instances in Jest or AVA

This post goes through how to use Object.defineProperty to mock how constructors create methods, ie. non-enumerable properties that are functions. The gist of Object.defineProperty use with a function value boils down to: const obj = {} Object.defineProperty(obj, 'yes', { ...

#Express #Node #jest #Testing #JavaScript

A testing guide for Express with request and response mocking/stubbing using Jest or sinon

To test an Express handler, it’s useful to know how to successfully mock/stub the request and response objects. The following examples will be written both using Jest and sinon (running in AVA). The rationale for this is the following. Jest is a very popular “all-in-one” testing ...

#Node #jest #testing #JavaScript #Sequelize

Mocking/stubbing ES6 classes in tests with examples of Sequelize model unit tests

This post goes through some patterns that can be used to unit test ES6 classes. The examples will use Jest module auto-mocking but should be portable to other module mocking libraries (eg. Proxyquire) with some modifications. In “Using ES6 classes for Sequelize 4 models&rdq ...

#Testing #JavaScript #ES6

When to use Jest snapshot tests: comprehensive use-cases and examples 📸

There’s some nice use-cases for snapshot tests outside of the well-travelled React/Vue UI component ones. In other words, although React and Vue testing with snapshots is pretty well documented, that’s not the only place they’re useful. As a rule of thumb, you c ...