Sinon.JS VS proxyquire

Mocha is a simple and flexible JavaScript testing framework for browser and Node.js applications. Unlike other testing frameworks, it takes a minimalist approach and relies on external libraries for key tasks. It uses Sinon for handling spies, stubs, and mocks, and Chai as the assertion engine. Mocha is extensible through many plugins and can integrate with most test runners.

As Obsidian code is not available; we must provide some alternate implementation. If you're familiar with sinon, you might think we can create a stubbed instance like this:

If you are using a mocking library, such as sinon, jest-mock, or ts-mockito, make sure that it is compatible with Jest. You may need to install additional packages or configure them in your configuration file. For example, to use sinon with Jest, you can install the sinon-jest package and add the following to your configuration file:

Mocha is a test runner, Chai is an assertion library, Sinon is a mocking library, this normally the combination you would need to use if you choose mocha, but there are others.

Instead, use pure functions + dependency inject your stubs (e.g. parameter to function). Also note, no need for Sinon or some other test double library. JavaScript is so good nowadays to easily make objects/classes/functions or any combination thereof on the fly that are terse.

I've had some good experiences with Ava + Sinon. I've personally disliked Jest because it seemed to do some weird trickery in the background that prevented me from using ES modules.

🤖 You can use the Mocha testing framework with the Chai assertion library to write tests for your Express controller. You can also use the Sinon library to mock the database calls. This will allow you to test the controller without actually making a call to the database. You can also use the SuperTest library to make HTTP requests to the controller and test the response.

You can use sinon js to create a mock version of your http library (axios) that responds with the data you’re expecting.

Assertions are the checkpoints of our test block that confirm if an automated test has passed or failed. Cypress bundles the Chai, jQuery, and Sinon.JS libraries for assertions. They check the desired, expected application in which the test is running. A complete listing of assertions can be found in the documentation here.

ES module is basically a "class" that you inject dependencies into through imports. And for tests you just use something like sinon to swap module dependencies for mocks.

Take a look at proxyquire: https://www.npmjs.com/package/proxyquire - they do some fancy magic to allow you to stub es module imports.

Now that we know how to call/execute a lambda function in our local. Let us learn about mocking the dependencies inside the lambda function. These dependencies can be any third-party libraries or DB call or even an API call. To override and mock these dependencies we can use proxyquire package.

I have been wary of this from when it first came about with rewire and similar libraries. As time has gone on my opinion has only strengthened, and with jest actively embracing mocking modules, I feel like nobody has even bothered to make a counter argument.

If you move foo to a different file and use something like proxyquire, you can override the require from that file to foo.js and sub in something else in the test.