With the implementation in place, let’s test it. Tests might make you feel more confident about your application. Writing Unit test cases with nest.js. Created for Monoliths and Micro-services (whole area in the paperwork concerning the Microservice kind of a … There are also, for example, integration tests and contract tests that can assure us the contracts (expected input/output values of the external dependencies) haven’t changed. A progressive Node.js framework for building efficient and scalable server-side applications.. LogRocket also monitors your app’s performance, reporting metrics like client CPU load, client memory usage, and more. Select npm and hit ENTER on your keyboard to start installing Nest.js. We have to write our code in books.controller.ts. In this post, we will begin with writing unit test cases for the mongodb.module.js file to test and write the functional code for its expected behaviour. Then, with jest.spyOn, we can mock the implementation of the get method of httpService. Thanks for catching that Lucas. The setup will always look somewhat the same because of the AAA (arrange, act, assert) pattern. Before writing the tests, let’s create the testing module. Now let’s take a look at a practical example: testing the aforementioned playlist module scenario. 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. To learn about the other things that Jest can test, see Using Matchers. Since objects in JavaScript are passed around by reference, we can easily override a specific method, like: But doing so by hand would be tiresome and error-prone. If you get timeouts or ECONNREFUSED errors, double-check that the emulator is actually running. Now that we wrote all our tests, we might want to check our test coverage. Jest provides us with a better way to do that: spies. “UNIT TESTING is a level of software testing where individual units/ components of a software are tested. Ideally, as your project becomes bigger you’ll want to create separate modules for your features (and corresponding controllers and services). It ensures that the function has the expected behavior when we control all the external dependencies. Controllers are where you’ll define your routes and call their corresponding services. Notice that one of the imported modules is the real HttpModule. It is a simple object that does nothing. More on setting up Jest with a more case-oriented config can be found in the docs. This test used expect and toBe to test that two values were exactly identical. 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 … Testing can be very time-consuming, so we should avoid at all costs over-engineering and losing time, right? 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. The backend is developed using the NestJS framework which uses Jest as testing tool. The first scenario is done. Having unit tests in place also helps during refactoring because we are sure we didn’t break anything while trying to improve our codebase. Since this is the first article of the course, we will briefly compare popular types of testing. A module usually contains more than one service and controller. Open this file, you will find the below code inside it: import { Controller } from '@nestjs/common'; @Controller('books') export class BooksController {} I am really stucked with writing unit test cases with nest.js. It's the simplest solution in our situation, because the mocked response will change for each test case. Not all logic needs to be tested! Basic NestJS architecture is composed of Modules, Controllers and Services. The purpose is to validate that each unit of the software performs as designed. If the answer is yes, you can simplify your tests. Use the @firebase/rules-unit-testing module to interact with the emulator that runs locally. The best practice is to test the result of your method, not the implementation details. Share in the comments! I'm going to After calling Jest’s .expect(value) method, an object containing Jest’s matches is returned. Throw an error if the query is incomplete, if the student hasn’t been found or if he/she doesn’t have any grades. Having a well tested backend is an important step for having a successful product. Learn everything from fundamentals, to more advanced topics such as authentication, microservices, GraphQL and much more. The best part? In this case, testing the output would be silly at best and wouldn’t really give us any confidence in whether the code is working as expected. Testing Mongoose model logic itself – such as validation 2. Tests for the three remaining methods — .updateOne() , .findOne(), and .removeOne() — look more or less the same. 12 min read Running said tests on each commit (locally) and on a CI service can greatly improve our confidence. 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. Most of the business logic is there, and you’ll want to make sure that neither a “future you” or someone else will break the beautiful code you’ve written today. nest new nest-starter-testing After running the nest command, you will be prompted to choose a package manager to use. But it is slow and needs a special setup, and thus, it is not really feasible to be run during development, which is when we usually run unit tests. Nest’s CLI-generated projects are automatically configured to run tests by simply typing npm run test in the terminal. Use “toBe” if you want the response to be the instance of the expected response. Isolating the logic from all the external dependencies is called mocking. Thankfully, Nest provides us with the @nestjs/testing package. When you start each chunk of logic of your code with a test that fails and then you write the minimal amount of code that makes it pass, you’re ensuring that you’re not over-engineering your app and that your tests are useful and reliable. I like to group tests in logical blocks that describe the action taking place — so, in this case, creating a playlist. As we mentioned before, … Assuming you already installed and configured mongoose in your NestJS project. It is really just creating scenarios in which the method would behave differently and then testing its expected behavior. 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). Since we don’t want to create an actual database connection, we are overriding the playlistRepository with PlaylistRepositoryFake. Services Testing. But with unit tests, we would rather not recreate the whole application for each test. Nest does not oblige developers to use Typescript, however, it fully supports it and we encourage you to use it! Unit Test 1: Reading MongoDBModule Object. But once you master the testing techniques I’ll show you, it’ll become very simple. 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). They will also prevent you from fixing the one thing while breaking another. After we call the method, we expect that the result is the playlist that was “saved” in the database. Typescript is a programming language that allows static typing and compiles to pure Javascript. Tests (unit testing, integration testing, and e2e testing) In a real scenario, speaking in terms of quantity, unit tests> integration tests> e2e tests. TDD is a development technique that lots of people have heard of (and even tried once), but don’t use that often. Usually, our functions internally make use of other functions. We strongly recommend using a recent version of Node.js so you can use async/await notation. In our StudentService unit test, we’ll mock AppService by creating an ApiServiceMock class. The API will provide a random squid gif when called. Would you recommend other steps to be a better tester? Hi, I have two components that need to talk to each other, to avoid the circular dependency issue, I'm using this.moduleRef.get on both components to access the instance methods.. In the test, we override the value that would normally be returned by the dependency. 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. Read more about how we chose ours. Bear in mind that this is a very basic setup that doesn’t necessarily reflect how an application should be structured. Besides all this, NestJS has one notable aspect: it offers its developers advantages to write automated tests. Although we are overriding the behavior of a method, Jest’s spies still require the provided object to have said property. Keeping the variables’ names structured like that helped me personally to keep my tests cleaner and more readable overall. NestJS is a server-side backend framework that is becoming increasingly popular within the Node community. You can also add ‘"verbose": true’ if you want more details into your test report. The getRepositoryToken function lets us get the injection token of the repository. This route will be used to exemplify two kinds of tests: unit and end-to-end. 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. Database persistence with MongoDB. If so, how would we deal with the types? 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. Unit testing NestJS applications. Nest (NestJS) is a framework for building efficient, scalable Node.js server-side applications. Dependency injection is usually based on interfaces rather than concrete classes. Easy of unit-testing applications. Nest’s CLI-generated projects are automatically configured to run tests by simply typing npm run test in the terminal. All of the methods are the most basic implementation of the CRUD behavior. 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. In this snippet, we use .mockResolvedValue() as opposed to .mockReturnValue() due to the original implementation returning a promise. We want to make sure that the mongodb.module.js file is a module that exposes an object. Unit tests are only interested in the logic that the function itself contains, not the external one. With Jest, it’s pretty simple: go to your package.json file, find the Jest configuration and add ‘"collectCoverage": true’ to it. ... NestJS is a Node.js back-end development framework built upon Express, leveraging the power of TypeScript. 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. 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. Although getting an application tested thoroughly is a complicated thing to do, unit testing is the easiest kind of testing to grasp. Each test first generates the fake data, then sets up spies, executes the method, and expects the result and the mocks to be a certain way. 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