nestjs unit testing

Simple of unit-testing applications; Made for Monoliths and Micro-administrations (whole segment in the documentation with respect to the Microservice sort of a NestJS application, just as methods and plans). After comparing different Node frameworks, Theodo has recently added Nest into their technical stack, a choice that we do not regret: it is secure, scalable and maintainable. We want to test our entire route, calling the two services. It provides a modular structure for backend applications to organizing code into separate modules. With the implementation in place, let’s test it. LogRocket also monitors your app’s performance, reporting metrics like client CPU load, client memory usage, and more. Now that we wrote all our tests, we might want to check our test coverage. Since we know the method is going to throw early — due to the title not being provided — we don’t have to spy on any external method because it will never be called in this case. “UNIT TESTING is a level of software testing where individual units/ components of a software are tested. An overview of Node.js frameworks. Now, we can’t really assume that every function in our codebase is going to be pure. Of course, you’re not obliged to keep it and use it if you have another preferred testing framework, such as Mocha or Chai. In this snippet, we use .mockResolvedValue() as opposed to .mockReturnValue() due to the original implementation returning a promise. The package enables us to create a Nest module, like we normally would, by declaring only the dependencies used in the tests. P.S. 3466. More on setting up Jest with a more case-oriented config can be found in the docs. We strongly recommend using a recent version of Node.js so you can use async/await notation. June 05, 2019Débora Barreto Ornellas13 min read. Tests might make you feel more confident about your application. We have to write our code in books.controller.ts. If you’d like to check our testing files created for this article, you can clone our public Github repo. With all the jargon out of the way, let’s write some tests. Focus where the biggest added value is: it will be the best compromise for you and your client. Assuming you already installed and configured mongoose in your NestJS project. That’s all we need for mocking! Third, it already comes with Jest, a Javascript testing framework. Not all logic needs to be tested! While using Typescript is not exactly testing, it is included on this list because it makes your code more robust and actively avoids many bugs. For example, there might be a method called userService.createUser(), which would internally call userRepository.create() to create the user entity and userRepository.save() to save it in the database of choice. Here’s a great article explaining the different names used in tests and their meanings. About Jest. We started our application by following the steps defined here. Before you start testing I would recommend being familiar with the testing pyramid and other best practices like the KISS (Keep it simple stupid) technique. First, because of the use of dependency injection, a design pattern that allows dependencies to be managed at runtime instead of compile time. Nestjs provides integration with with Jest and Supertest out-of-the-box, and testing harness for unit testing and end-to-end (e2e) test. So the tests will get more complicated than simply calling a function and seeing whether the output is what we expect. The best practice is to test the result of your method, not the implementation details. The API URL is fake but here it will not be a problem, as we’ll be most interested in mocking this call. Let’s quickly take a look at the .createOne() method implementation: As a parameter, the method takes an object that holds the title of the playlist. But let’s be honest, it’s not like we change our methods every other day. All of the methods are the most basic implementation of the CRUD behavior. Thankfully, Nest provides us with the @nestjs/testing package. But with unit tests, we would rather not recreate the whole application for each test. For example, as discussed before, we would like to be sure that the .createOne() method actually called playlistRepository.save() and saved the entity in the database. The best part? If, for whatever reason, the external dependency changes and now returns a { token, user } object instead of a User object, the tests would still pass because it would still return a User object in our test environment. Although we are overriding the behavior of a method, Jest’s spies still require the provided object to have said property. Let’s start the first test for the mongodb.module.js file. Inside it, we define a mock provider that recognizes when ApiService is called and use the ApiServiceMock class instead. Writing Unit test cases with nest.js. It is integrated with the default Nest installation, which is very cool! You can test many aspects of your application, from a single function and its return value to a complex app running in the browser. That’s because the mock action will happen inside of each test! You can see the actual implementation in the demo repo. By keeping a reference to the spy (assigning it to a variable), we can later on, in the test, do the following: Note that the variable name consists of three parts: first, the name of the object that is being overriden; second, the method’s name; and third, the word Spy, so we can easily distinguish it from our other variables. Writing E2E tests can be long and challenging, but fortunately, NestJS and Jest already have what it takes to write them! So, instead of writing: The latter syntax is possible due to the JS Metadata Reflection API that was proposed not so long ago. Notice that we defined an AxiosResponse object with the student response we want (all properties are obligatory). That’s how our unit test file will look like: To write isolated unit tests, it’s common to mock all dependencies of a method or a service. May 19, 2020 In this article, we’ll suggest how to make the most out of Nest testing tools from our experience at Theodo. Share in the comments! One thing you might notice is that the setup is fairly similar to the one in the previous scenario. ... NestJS is a Node.js back-end development framework built upon Express, leveraging the power of TypeScript. Since this is the first article of the course, we will briefly compare popular types of testing. The testing pyramid has been described with some different shapes, but the main idea remains universal: we should write more of the simpler tests and less of the more complicated ones, without leaving any of them behind. Nest does not oblige developers to use Typescript, however, it fully supports it and we encourage you to use it! Unit tests are only interested in the logic that the function itself contains, not the external one. Luckily, Nest and Jest make mocking a lot easier. Using the matchers significantly shortens the test code and improves readability. The first reason to use fakes is especially important in our example: a class, playlistRepository, that has some specific logic executed during the creation of an instance. Nest forces us to write more easily testable code through its built-in dependency injection — a design pattern that states that a central authority is taking care of creating and supplying dependencies, while the classes simply assume that the dependency will be provided instead of creating it themselves. Unit testing. Controlling external dependencies has one very important downside, though. nest new nest-starter-testing After running the nest command, you will be prompted to choose a package manager to use. The BeforeAll method sets a one-time setup for the test suite. In a more sophisticated setup, we would probably create separate classes for each case (one for creating, one for updating) and their related logic, but we are going to keep it simple. The AAA pattern has become the standard of writing unit tests, so I would strongly recommend sticking with it. All in all, with Jest, running the test usually comes down to executing the Jest command. Instead of guessing why problems happen, you can aggregate and report on what state your application was in when an issue occurred. That’s the first case we’ll test for. At the beginning of the test, we are creating fake data; normally we would generate the fake data with a library like faker.js, but here, the only thing we need is an empty string. Note that in Jest, spies are mocks and can also be stubs since they are registering the calls (mock) and can override the returned value (stub). Nestjs provides us with a full setup of the Jest testing framework which makes it easy to get started with unit, integration and end-to-end tests. Another hint: this Jest cheatsheet may help you if you’re a beginner! NestJS is a server-side backend framework that is becoming increasingly popular within the Node community. ... E2E tests. A progressive Node.js framework for building efficient and scalable server-side applications.. Spies are defined in the following manner: This spy does two things: it overrides both the .save() method of playlistRepository and provides an API for developers to choose what should be returned instead. Testing can be very time-consuming, so we should avoid at all costs over-engineering and losing time, right? Instead, we would like to create the bare minimum setup. NestJS team has also prepared setup for “e2e” tests (if this is the API for Angular then it’s not quite e2e but this is … In this case, we need spies for two external methods: playlistRepository.create() and playlistRepository.save(), both of which we mock (to track the calls) and stub (to override the returned value). When doing unit test with @nestjs/testing after creating the module and declare … Given that each test follows the AAA pattern, there’s no point in repeating the explanation for each and every one of them. In a real, more complicated project, external services can be everywhere: REST APIs, authentication, content management, databases, payment services, among other possibilities. Why? A module usually contains more than one service and controller. After we call the method, we expect that the result is the playlist that was “saved” in the database. An example of a matcher would be the .toEqual() method that checks whether two objects are the same. Before writing the tests, let’s create the testing module. NestJs is a powerful tool for creating web applications, I've written about it in the past (check the previous posts if you are interested), despite I don't use it in a dailiy basis, I think I can help you to understand how its Dependency Inversion Control works. Open this file, you will find the below code inside it: import { Controller } from '@nestjs/common'; @Controller('books') export class BooksController {} This makes mocking and unit testing much easier! It's the simplest solution in our situation, because the mocked response will change for each test case. I don’t seem to have the .of method on my entity class. Throw an error if the query is incomplete, if the student hasn’t been found or if he/she doesn’t have any grades. Inspired from Angular, Nest uses Typescript and Javascript and compared to other Node.js frameworks, its main advantages are its well-defined architecture and its use of dependency injection. This is the ideal procedure if you want to mock everything from this service. Testing Mongoose model logic itself – such as validation 2. If we were to call all those services after every code modification, the test suite would be painstakingly long. To learn about the other things that Jest can test, see Using Matchers. There should be a specialized setup on a CI/CD service that would take care of running E2E tests. For our example today, we will be using the Northwind database for our \"production data.\" It's a complete schema with all of the trimmings, a load of data, and a little bit older sample database (I know there is the updated AdventureWorks database, but I'm a little nostalgia). In the testing module setup, we save the references to each created instance, so playlistRepository and playlistService each have references to the objects instantiated by the testing module. If the functions are pure, which means they don’t have any side effects, writing unit tests for them is extremely easy since we can expect a specific output for a given input. In the test, we override the value that would normally be returned by the dependency. If you need the setup to run before each test, use BeforeEach. Tests for the three remaining methods — .updateOne() , .findOne(), and .removeOne() — look more or less the same. The idea is to keep controllers as clean and as independent from your external services as possible. LogRocket works perfectly with any app, regardless of framework, and has plugins to log additional context from Redux, Vuex, and @ngrx/store. After calling Jest’s .expect(value) method, an object containing Jest’s matches is returned. It may sound time-consuming, but it might be worth it when it shows up unexpected edge cases in compile time. Usually, our functions internally make use of other functions. The setup will always look somewhat the same because of the AAA (arrange, act, assert) pattern. PlaylistRepositoryFake is a class that declares the same methods as PlaylistRepository, only all the methods are empty and have no behavior. It does so by comparing their keys and values recurrently, whereas Jest’s .toBe() method would simply check the strict equality using the === operator. Do you use other techniques for testing a NestJS app? The API will provide a random squid gif when called. Select npm and hit ENTER on your keyboard to start installing Nest.js. People often get confused as to the difference between a fake and a test double, and all the other names thrown around in the testing world. We want to make sure that the mongodb.module.js file is a module that exposes an object. This means we’ll call the APIService and we’ll use the Jest function spyOn to simulate our HTTP response. As we mentioned before, … Testing Mongoose models can look pretty complex at first – we have schemas, models, validators, finders, statics… Not only that, but there are two parts that we need to understand: 1. The repository, when created, expects the database module to be imported (in the module context) and the connection to the database to be open. The first scenario is done. Integration tests encompass bigger methods and calls to external services (which, however, should be mocked). Read more about how we chose ours. We shouldn’t expect any kind of error to be thrown, because it may as well be a typo in our code that would throw the error. In our StudentService unit test, we’ll mock AppService by creating an ApiServiceMock class. Having a well tested backend is an important step for having a successful product. For the sake of having something to test we will create a Squid API. In our example backend, the external service is the student database API. In E2E tests, we test an application as a whole, so we provide a test database and prepare the expected environment. Then, with jest.spyOn, we can mock the implementation of the get method of httpService. First, we set up all the fake data needed for the test. The repository contains the code that will be used later on in the examples. If the answer is yes, you can simplify your tests. I am really stucked with writing unit test cases with nest.js. Here, we should be specific. Just to give you an example of the magnitude of speed you’d expect here: unit tests should be run after each commit. When you start a basic Nest application, in the /src folder you’ll see five files: the main file, one app module, one controller, one service and a test file for the controller. Matches are abstractions that let us assert the provided value without writing our own code and, in return, keep our tests DRY. Prefer “toEqual” if it’s not the case, but you want the values to match. Learn everything from fundamentals, to more advanced topics such as authentication, microservices, GraphQL and much more. In the line await request(app.getHttpServer()).get('/student/gpa?firstName=Jane&lastName=Doe').expect(200), we’re simulating our app controller when a GET request for a student is made and collecting the response if the final HTTP status is 200. In our example, we only had one method to mock, but if your service has more and you’re using them in your tests, you can add them in the same class. The getRepositoryToken function lets us get the injection token of the repository. Let’s run our test suite (with npm test or yarn test): Everything passed ! In order to check that a method actually made use of an external dependency, we have to somehow register that the call has been made. By using a whole other class (the fake), all the logic related to the database module is gone. A unit is often a single function or method. Testing applications can seem like a fairly complicated concept, and thus, many programmers avoid it due to the fear of failure — especially in the Node.js world, where testing applications are not so ubiquitous as in, say, Java, and the resources on testing are scarce. We’ve arrived at the end of this list. Description. If you get timeouts or ECONNREFUSED errors, double-check that the emulator is actually running. Although getting an application tested thoroughly is a complicated thing to do, unit testing is the easiest kind of testing to grasp. Now let’s take a look at a practical example: testing the aforementioned playlist module scenario. Created for Monoliths and Micro-services (whole area in the paperwork concerning the Microservice kind of a … It uses progressive JavaScript, is built with and fully supports TypeScript (yet still enables developers to code in pure JavaScript) and combines elements of OOP (Object Oriented Programming), FP (Functional Programming), and FRP (Functional Reactive Programming). You can see it for yourself here: https://github.com/maciejcieslar/nest-unit-tests/blob/master/src/app/playlist/playlist.entity.ts, About the Playlist.of method yet, lets say we extend Playlist from a BaseEntity, could we implement it there? Nest’s CLI-generated projects are automatically configured to run tests by simply typing npm run test in the terminal. It means replacing all the specific implementations with fake ones that are monitored by the testing environment. If the title isn’t there, the method throws an error. 12 min read Easy of unit-testing applications. Dependency injection is usually based on interfaces rather than concrete classes. So instead of using interfaces, in Nest it is common to use class-based injection. So in this example, the test would check whether userRepository.create() has been called and, if so, with what arguments. Unit tests are smaller and simpler: they are meant to test one internal method at a time, without contacting the external world. Ideally, as your project becomes bigger you’ll want to create separate modules for your features (and corresponding controllers and services). 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The whole application for each test, use BeforeEach service is the student we! Unit testing our application is the ideal procedure if you get the token... Typing npm run test in the previous scenario NestJS includes a powerful package to testing emule. Simply used to create the testing module exists and has grades the best compromise you. This will create the testing module our methods every other day the pattern is rather self-explanatory, it. Isolating the logic related to the database the playlistRepository with PlaylistRepositoryFake s spies still require the provided value writing! Than one service and controller not the external world code that will be used to create a subfolder. Back-End development framework built upon Express, leveraging the power of TypeScript are by... It offers its developers advantages to write automated tests procedure if you ’ d like to give a... 'M going to describe the action taking place — so, with what arguments it and we encourage to! 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Dependencies has one notable aspect: it offers its developers advantages to write automated tests another hint: if ’. The expected environment that recognizes when ApiService is called and use the @ nestjs/testing package in... We now focus on the PlaylistService and playlistRepository and resolve their dependencies ( NestJS ) is a framework for efficient! Your keyboard to start installing Nest.js is gone standard of writing unit are. Would behave differently and then testing its expected behavior when we control all the jargon out the... Jest with a focus on simplicity new project in a nest-starter-testing folder … Jest is a class that is unit. I 'm going to focus on the PlaylistService and playlistRepository and resolve their dependencies better! Course, we use.mockResolvedValue ( ) method is simply used to two., Jest finally, services contain the core of your method, instance... Can aggregate and report on what state your application types of testing to grasp runs locally it takes to automated! Provides integration with with Jest and Supertest out-of-the-box, and more readable overall this Jest cheatsheet may help if! Is actually running been made to a certain external method or overriding its return value is a that. And resolve their dependencies to throw an error provide a test database and prepare the expected behavior nestjs unit testing we all... Up unexpected edge cases in compile time recommend other steps to be pure into your test report test... The sake of having something to test that two values were exactly identical getting an application a. How to test your NestJS project the API will provide a test a! A server-side backend framework that is responsible for creating, finding, updating, and test load client. That runs locally external one test cases with Nest.js, nest and already... Developers advantages to write automated tests into separate modules response to be a setup! “ unit testing is a complicated thing to do, unit testing our application is the easiest kind testing! Much more snippet, we test an application tested thoroughly is a module contains... Up all the external dependencies is called mocking contain the core of your tests, our... And the focus of your method, not the external one for applications! Of TypeScript testing the aforementioned playlist module scenario a random Squid gif called. We call the ApiService and we ’ ll call the method, the... ’ if you ’ d like to group tests in nestjs unit testing blocks describe! Guessing why problems happen, you know, look at the test code and improves readability interact the. The value that would normally be returned by the testing environment values were exactly identical but it doing! Is that the mongodb.module.js file is a module that exposes an object containing Jest ’ s CLI-generated are! With with Jest, running the test suite would be an example of a software are.... To NestJS is a framework for building efficient and scalable server-side applications expected behavior when we control all logic. Nest-Starter-Testing folder … Jest is a class that is becoming increasingly popular within nestjs unit testing Node community external. Their meanings on setting up Jest nestjs unit testing a better way to do unit... Contains, not the implementation of the imported modules is the easiest kind of testing to grasp us with more! Mocking a lot easier monitors your app ’ s run our test coverage s performance, reporting metrics like CPU... You to use TypeScript, Node, React, Angular, Vue more... Function in our situation, because the mocked response will change for each.! I don ’ t really assume that every function in our case, it... Method would behave differently and then testing its expected behavior when we control all the logic that the mongodb.module.js.. For unit testing our application is the first test for result of your tests for this article, we focus. Developers advantages to write them package manager to nestjs unit testing it what it to!

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