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Introduction to Testing in Node.js with Mocha and Chai

When writing software, it can be tedious to test features manually and ensure your entire program continues to work as it evolves over time. We can use automated testing to invoke our program automatically, and ensure it works as expected.

The Purpose of Testing

Simply put, writing good tests that verify your program works as expected will help you catch regressions, and improve the reliability of your software. Good tests will ensure the program meets the requirements the program needs to meet, and that it will continue to do so as the program evolves over time. Software testing is also integral to some software development processes like TDD and BDD, though these are outside the scope of this article.

The Node.js ecosystem has a large variety of testing frameworks to choose from, and many serve many different purposes. We'll be focusing on using Mocha and Chai to demonstrate the basics of testing in the context of backend development.

What are Mocha and Chai?

Mocha is a JavaScript testing framework that runs on Node.js, and in the browser. It is one of the most popular test frameworks in use in the Node.js community, and is very easy to learn and understand.

Chai is an assertion library that helps extend test frameworks like Mocha to make writing certain kinds of tests easier. Most test frameworks like Mocha also come with their own assertion functions as well, but we've opted to show off Chai since it makes it easier to write more complex tests.

Installing Mocha and Friends

Mocha and Chai can be installed into your project using the following:

npm install mocha chai --save-dev

Also, note that all following examples are available on GitHub for your viewing pleasure. I won't be showing all code being tested in this article as it would be a lot. You can then define a scripts section in your package.json file to run your tests so you can run your tests with npm test.

{
  "name": "mocha-basic",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "mocha"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "mocha": "^8.3.2"
  }
}

The Basics

We will start by showing off one of the most basic tests that you can make with Mocha, and bear with me as I'll show off some more complex tests later. This is a basic unit test that calls a function that returns the number 42, and tests that the result comes back as expected. The following is defined in a file called index.js.

exports.meaningOfLife = () => {
  return 42;
};

And the test for this function can be written as follows in a file located at test/index.test.js (note the naming convention).

const assert = require("assert");

const { meaningOfLife } = require("../index");

describe("Index", function () {
  describe("#meaningOfLife", function () {
    it("should return 42", function () {
      const result = meaningOfLife();
      assert.strictEqual(result, 42);
    });
  });
});

Tests can be run by invoking npm test in your project root. I've opted to keep all tests in a directory called test under the project root, and have test files for each corresponding source file with an added test.js suffix at the end of the filename. There are a few layers to this test, so let's go through each one.

Tests are defined by calling global Mocha functions that are defined when the mocha command is invoked. describe is used for organizing your tests. The way that I'm using it above is one level for what I'm testing in general, this being the index file, the meaningOfLife function, and then all tests that need to invoke that function. In this case there's only one test since this is a very simple function.

Tests are written inside of callbacks passed into the it function. One thing to note is how the test reads out like plain English. This is meant to make the purpose of the test to be more clear to the reader. In this example, we simply import and call the meaningOfLife function and check that it equals 42. We also use the assert call from Mocha to do this comparison, as it will raise an exception if the two expressions don't match.

Let's test an API

To demonstrate more practical tests, I've opted to create a basic API that returns data, and tests that the data has the expected format. The API is a simple express application that returns an array of movies as JSON by calling GET /movies against it.

Testing an API isn't as simple as calling a function, and checking a response, so we will use chai and supertest to help us. The tests are as follows:

const chai = require("chai");
const request = require("supertest");

const expect = chai.expect;
const app = require("../../app");

describe("Movies", function () {
  describe("GET /movies", function () {
    it("should return 200 OK with several movies", async function () {
      const response = await request(app)
        .get("/movies")
        .expect(200)
        .expect("Content-Type", /json/);

      const movies = response.body;
      expect(movies).to.be.an("array");
      expect(movies).length.to.be.greaterThan(0);
    });

    it("should have valid movies", async function () {
      const response = await request(app)
        .get("/movies")
        .expect(200)
        .expect("Content-Type", /json/);

      const movies = response.body;
      expect(movies).to.be.an("array");

      movies.forEach(movie => {
        expect(movie.name).to.be.a("string");
        expect(movie.year).to.be.a("number");
        expect(movie.rating).to.be.a("number");
        expect(movie.description).to.be.a("string");
        expect(movie.director).to.be.a("string");
        expect(movie.genres).to.be.an("array");
      });
    });
  });
});

Chai, as mentioned before, is an assertion library, and we use it here primarily for type checking the data coming back from the API. We use SuperTest to make API calls. We pass our app object to SuperTest, and it handles making sure the API is listening, and gives us access to some useful HTTP request builders that include assertion functions as well.

We import the expect function from Chai, and use it instead of the built-in Mocha ones. The tests read out like plain English, and are very easy to understand. Chai actually has several interfaces that allow you to write tests such as "should" and "assert". These are detailed on their website.

Hooks

Imagine that the API we're testing has a persistent database of some kind. The data stored in these database will naturally persist between tests, and this can be bad if we want tests to be reproducible. To solve this problem, we can use hooks. Hooks allow code to be run before and after test blocks.

In this case we want to use them to initialize and destroy the database the API will be using for each test to ensure the state is consistent every time a test is run, and will always have the same result.

Here is an example of the beforeEach and afterEach hooks in action.

const chai = require("chai");
const request = require("supertest");

const expect = chai.expect;
const app = require("../../app");
const db = require("../../db");

describe("Movies", function () {
  // Create the schema before each test in the describe block.
  beforeEach(async function () {
    const database = await db.database;
    await db.initDB(database);
  });

  // Drop the schema before each test in the describe block.
  afterEach(async function () {
    const database = await db.database;
    await db.resetDB(database);
  });

  describe("GET /movies", function () {
    it("should return 200 OK with several movies", async function () {
      ...
    });

    it("should have valid movies", async function () {
      ...
    });
  });

  describe("GET /movies/:id", function () {
    it("should query an individual movie", async function () {
      ...
    });
  });

  describe("POST /movies", function () {
    it("should create a new movie", async function () {
      ...
    });
  });

  describe("PATCH /movies/:id", function () {
    it("should update an existing movie", async function () {
      ...
    });
  });

  describe("DELETE /movies/:id", function () {
    it("should delete an existing movie", async function () {
      ...
    });
  });
});

I've removed the contents of the actual tests since they're a bit long, but they're in the GitHub repository if you're curious. The details of the db and app modules are outside the context of this article.

The main takeaway here is the code inside of the beforeEach hook will tell Mocha to create the database before each test, and the code in the afterEach hook will tell Mocha to destroy the database after each test. I should also mention it and describe are also hooks as well!

Mocha Hooks:

  • it: Defines a single test.
  • describe: Defines a block of tests.
  • before: Run only once before the first test in the describe block.
  • after: Run only once after the last test in the describe block.
  • beforeEach: Runs before every test in the describe block.
  • afterEach: Runs after every test in the describe block.

Conclusion

Effective use of testing libraries in Node.js like Mocha and Chai can help make it easy to write tests and make your application more reliable. The example projects used throughout this article can be found on my GitHub. I have only scratched the surface here when it comes to testing. There are also frontend testing frameworks such as Selenium and Cypress. We've actually written about Cypress on our blog as well, and you can find that here if you're curious.

This Dot Labs is a development consultancy that is trusted by top industry companies, including Stripe, Xero, Wikimedia, Docusign, and Twilio. This Dot takes a hands-on approach by providing tailored development strategies to help you approach your most pressing challenges with clarity and confidence. Whether it's bridging the gap between business and technology or modernizing legacy systems, you’ll find a breadth of experience and knowledge you need. Check out how This Dot Labs can empower your tech journey.

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Angular 17: Continuing the Renaissance

Angular 17: A New Era November 8th marked a significant milestone in the world of Angular with the release of Angular 17. This wasn't just any ordinary update; it was a leap forward, signifying a new chapter for the popular framework. But what made this release truly stand out was the unveiling of Angular's revamped website, complete with a fresh brand identity and a new logo. This significant transformation represents the evolving nature of Angular, aligning with the modern demands of web development. To commemorate this launch, we also hosted a release afterparty, where we went deep into its new features with Minko Gechev from the Angular core team, and Google Developer Experts (GDEs) Brandon Roberts, Deborah Kurata, and Enea Jahollari. But what exactly are these notable new features in the latest version? Let's dive in and explore. 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Understanding Vue's Reactive Data

Introduction Web development has always been about creating dynamic experiences. One of the biggest challenges developers face is managing how data changes over time and reflecting these changes in the UI promptly and accurately. This is where Vue.js, one of the most popular JavaScript frameworks, excels with its powerful reactive data system. In this article, we dig into the heart of Vue's reactivity system. We unravel how it perfectly syncs your application UI with the underlying data state, allowing for a seamless user experience. Whether new to Vue or looking to deepen your understanding, this guide will provide a clear and concise overview of Vue's reactivity, empowering you to build more efficient and responsive Vue 3 applications. So, let’s kick off and embark on this journey to decode Vue's reactive data system. What is Vue's Reactive Data? What does it mean for data to be ”'reactive”? 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Here, the keys represent our properties (in our case, that would be `message` and `showSword`), and the values correspond to their effects – remember, they are stored in a Set that in Vue 3 we refer to as `dep`. Huh… It might seem a bit complex, right? Let's make it more straightforward with a visual example: With the above explained, let’s see what this Track` method kind of looks like and how it uses this `targetMap`. This method essentially is doing something like this: `javascript let activeEffect; // we will see more of this later function track(target, key) { if (activeEffect) { // depsMap` maps targets to their keys and dependent effects let depsMap = targetMap.get(target); // If we don't have a depsMap for this target in our targetMap`, create one. if (!depsMap) { depsMap = new Map(); targetMap.set(target, depsMap); } let dep = depsMap.get(key); if (!dep) { // If we don't have a set of effects for this key in our depsMap`, create one. dep = new Set(); depsMap.set(key, dep); } // Add the current effect as a dependency dep.add(activeEffect); } } ` At this point, you have to be wondering, how does Vue 3 know what activeEffect` should run? Vue 3 keeps track of the currently running effect by using a global variable. 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Take this.") { state.showSword = true; } }); ` This method behind the scenes is doing something similar to this: `javascript function effect(update) { //the function we are passing in const effectMethod = () => { // Assign the effect as our activeEffect` activeEffect = effectMethod // Runs the actual method, also triggering the get` trap inside our proxy update(); // Clean the activeEffect after our Effect has finished activeEffect = null } effectMethod() } ` The handling of activeEffect` within Vue's reactivity system is a dance of careful timing, scoping, and context preservation. Let’s go step by step on how this is working all together. When we run our `Effect` method for the first time, we call the `get` trap of the Proxy. `javascript function effect(update) const effectMethod = () => { // Storing our active effect activeEffect = effectMethod // Running the effect update() ... } ... } effect(() => { // we call the the get` trap when getting our `state.message` if (state.message === "It's dangerous to go alone! Take this.") { state.showSword = true; } }); ` When running the get` trap, we have our `activeEffect` so we can store it as a dependency. `javascript function reactive(obj) { return new Proxy(obj, { // Gets called when our effect runs get(target, key) { track(target, key) // Saves the effect return target[key] }, // ... (other handlers) }) } function track(target, key) { if (activeEffect) { //... rest of the code // Add the current effect as a dependency dep.add(activeEffect); } } ` This coordination ensures that when a reactive property is accessed within an effect, the track function knows which effect is responsible for that access. Trigger Method Our last method makes this Reactive system to be complete. 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A Guide to Custom Angular Attribute Directives cover image

A Guide to Custom Angular Attribute Directives

When working inside of Angular applications you may have noticed special attributes such as NgClass, NgStyle and NgModel. These are special attributes that you can add to elements and components that are known as attribute directives. In this article, I will cover how these attributes are created and show a couple of examples. What are Attribute Directives? Angular directives are special constructs that allow modification of HTML elements and components. Attribute directives are also applied through attributes, hence the name. There exist other types of directives such as structural directives as well, but we’re just going to focus on attribute directives. If you’ve used Angular before then you have almost certainly used a couple of the attribute directives I mentioned earlier before. You are not limited to just the built-in directives though. Angular allows you to create your own! Creating Attribute Directives Directives can be created using code generation via the ng CLI tool. ` ng generate directive ` This will create a file to house your directive and also an accompanying test file as well. The contents of the directive are very barebones to start with. Let’s take a look. ` import { Directive } from '@angular/core'; @Directive({ selector: '[appExample]', }) export class ExampleDirective { constructor() {} } ` You will see here that directives are created using a @Directive decorator. The selector in this case is the name of the attribute as it is intended to be used in your templates. The square brackets around the name make it an attribute selector, which is what we want for a custom attribute directive. I would also recommend that a prefix is always used for directive names to minimize the risk of conflicts. It should also go without saying to avoid using the ng prefix for custom directives to avoid confusion. Now, let’s go over the lifecycle of a directive. The constructor is called with a reference to the ElementRef that the directive was bound to. You can do any initialization here if needed. This element reference is dependency injected, and will be available outside the constructor as well. You can also set up @HostListener handlers if you need to add functionality that runs in response to user interaction with the element or component, and @Input properties if you need to pass data to the directive. Click Away Directive One useful directive that doesn’t come standard is a click away directive. This is one that I have used before in my projects, and is very easy to understand. This directive uses host listeners to listen for user input, and determine whether the element that directive is attached to should be visible or not after the click event occurs. ` @Directive({ selector: '[appClickAway]', }) export class ClickAwayDirective { @Output() onClickAway: EventEmitter = new EventEmitter(); constructor(private elementRef: ElementRef) {} @HostListener('document:click', ['$event']) onClick(event: PointerEvent): void { if (!this.elementRef.nativeElement.contains(event.target)) { this.onClickAway.emit(event); } } } ` There are a few new things in this directive we’ll briefly go over. The first thing is the event emitter output onClickAway. A generic directive isn’t going to know how to handle click away behavior by itself as this will change based on your use case when using the directive. To solve this issue, we make the directive emit an event that the user of the directive can listen for. The other part is the click handler. We use @HostListener to attach a click handler so we can run our click away logic whenever clicks are done. The one interesting thing about this directive is that it listens to all click events since we’ve specified ‘document’ in the first parameter. The reason for this is because we care about listening for clicking anything that isn’t the element or component that the directive is attached to. If we didn’t do this, then the event handler would only fire when clicking on the component the directive is attached to, which defeats the purpose of a click away handler. Once we’ve determined the element was not clicked, we emit the aforementioned event. Using this directive makes it trivial to implement click away functionality for both modals and context menus alike. If we have a custom dialog component we could hook it up like this: ` Dialog Box This is a paragraph with content! ` If you want to see this directive in action, then you can find it in our blog demos repo here. Drag and Drop Directive Another useful directive is one that assists with drag and drop operations. The following directive makes elements draggable, and executes a function with a reference to the location where the element was dragged to. ` @Directive({ selector: '[appDragDrop]', }) export class DragDropDirective implements OnInit, OnDestroy { @Output() onDragDrop: EventEmitter = new EventEmitter(); mouseDown$ = new Subject(); mouseUp$ = new Subject(); destroy$ = new Subject(); constructor(private elementRef: ElementRef) {} ngOnInit(): void { this.mouseDown$ .pipe(takeUntil(this.destroy$)) .pipe(exhaustMap(() => this.mouseUp$.pipe(take(1)))) .subscribe((event) => { if ( event.target && event.target instanceof Element && !this.elementRef.nativeElement.contains(event.target) ) { this.onDragDrop.emit(event); } }); } ngOnDestroy(): void { this.destroy$.next(null); this.destroy$.complete(); } @HostListener('mousedown', ['$event']) onMouseDown(event: MouseEvent): void { this.mouseDown$.next(event); } @HostListener('document:mouseup', ['$event']) onMouseUp(event: MouseEvent): void { this.mouseUp$.next(event); } } ` Just like the previous directive example an event emitter is used so the user of the directive can associate custom functionality with it. RxJs is also utilized for the drag and drop detection. This directive uses the exhaustMap function to create an observable that emits both after a mouse down, and finally a mouse up is done. With that observable, we can subscribe to it and call the drag and drop callback so long as the element that’s dragged on isn’t the component itself. Note how the mouse down event is local to the component while the mouse up event is attached to the document. For mouse down, this is done since we only want the start of the dragging to be initiated from clicking the component itself. The mouse up must listen to the document since the dragging has to end on something that isn’t the component that we’re dragging. Just like the previous directive, we simply need to reference the attribute and register an event handler. ` Drag me over something! ` Conclusion In this article, we have learned how to write our own custom attribute directives and demonstrated a couple of practical examples of directives you might use or encounter in the real world. I hope you found this introduction to directives useful, and that it helps you with writing your own directives in the future! You can find the examples shown here in our blog demos repository if you want to use them yourself....

Testing a Fastify app with the NodeJS test runner cover image

Testing a Fastify app with the NodeJS test runner

Introduction Node.js has shipped a built-in test runner for a couple of major versions. Since its release I haven’t heard much about it so I decided to try it out on a simple Fastify API server application that I was working on. It turns out, it’s pretty good! It’s also really nice to start testing a node application without dealing with the hassle of installing some additional dependencies and managing more configurations. Since it’s got my stamp of approval, why not write a post about it? In this post, we will hit the highlights of the testing API and write some basic but real-life tests for an API server. This server will be built with Fastify, a plugin-centric API framework. They have some good documentation on testing that should make this pretty easy. We’ll also add a SQL driver for the plugin we will test. Setup Let's set up our simple API server by creating a new project, adding our dependencies, and creating some files. Ensure you’re running node v20 or greater (Test runner is a stable API as of the 20 major releases) Overview `index.js` - node entry that initializes our Fastify app and listens for incoming http requests on port 3001 `app.js` - this file exports a function that creates and returns our Fastify application instance `sql-plugin.js` - a Fastify plugin that sets up and connects to a SQL driver and makes it available on our app instance Application Code A simple first test For our first test we will just test our servers index route. If you recall from the app.js` code above, our index route returns a 501 response for “not implemented”. In this test, we're using the createApp` function to create a new instance of our Fastify app, and then using the `inject` method from the Fastify API to make a request to the `/` route. We import our test utilities directly from the node. Notice we can pass async functions to our test to use async/await. Node’s assert API has been around for a long time, this is what we are using to make our test assertions. To run this test, we can use the following command: By default the Node.js test runner uses the TAP reporter. You can configure it using other reporters or even create your own custom reporters for it to use. Testing our SQL plugin Next, let's take a look at how to test our Fastify Postgres plugin. This one is a bit more involved and gives us an opportunity to use more of the test runner features. In this example, we are using a feature called Subtests. This simply means when nested tests inside of a top-level test. In our top-level test call, we get a test parameter t` that we call methods on in our nested test structure. In this example, we use `t.beforeEach` to create a new Fastify app instance for each test, and call the `test` method to register our nested tests. Along with `beforeEach` the other methods you might expect are also available: `afterEach`, `before`, `after`. Since we don’t want to connect to our Postgres database in our tests, we are using the available Mocking API to mock out the client. This was the API that I was most excited to see included in the Node Test Runner. After the basics, you almost always need to mock some functions, methods, or libraries in your tests. After trying this feature, it works easily and as expected, I was confident that I could get pretty far testing with the new Node.js core API’s. Since my plugin only uses the end method of the Postgres driver, it’s the only method I provide a mock function for. Our second test confirms that it gets called when our Fastify server is shutting down. Additional features A lot of other features that are common in other popular testing frameworks are also available. Test styles and methods Along with our basic test` based tests we used for our Fastify plugins - `test` also includes `skip`, `todo`, and `only` methods. They are for what you would expect based on the names, skipping or only running certain tests, and work-in-progress tests. If you prefer, you also have the option of using the describe` → `it` test syntax. They both come with the same methods as `test` and I think it really comes down to a matter of personal preference. Test coverage This might be the deal breaker for some since this feature is still experimental. As popular as test coverage reporting is, I expect this API to be finalized and become stable in an upcoming version. Since this isn’t something that’s being shipped for the end user though, I say go for it. What’s the worst that could happen really? Other CLI flags —watch` - https://nodejs.org/dist/latest-v20.x/docs/api/cli.html#--watch —test-name-pattern` - https://nodejs.org/dist/latest-v20.x/docs/api/cli.html#--test-name-pattern TypeScript support You can use a loader like you would for a regular node application to execute TypeScript files. Some popular examples are tsx` and `ts-node`. In practice, I found that this currently doesn’t work well since the test runner only looks for JS file types. After digging in I found that they added support to locate your test files via a glob string but it won’t be available until the next major version release. Conclusion The built-in test runner is a lot more comprehensive than I expected it to be. I was able to easily write some real-world tests for my application. If you don’t mind some of the features like coverage reporting being experimental, you can get pretty far without installing any additional dependencies. The biggest deal breaker on many projects at this point, in my opinion, is the lack of straightforward TypeScript support. This is the test command that I ended up with in my application: I’ll be honest, I stole this from a GitHub issue thread and I don’t know exactly how it works (but it does). If TypeScript is a requirement, maybe stick with Jest or Vitest for now 🙂...