If you’ve heard the term “mock object”, this is the same thing — Sinon’s mocks can be used to replace whole objects and alter their behavior similar to stubbing … apiKeyToUser is just a lookup from apiKeys to usernames. We’ll look at some of the patterns it encourages and why they’ll bring you struggles down the road as well a simple, single-file, no-dependency way to define your configuration. In this article, we’ll show you the differences between spies, stubs and mocks, when and how to use them, and give you a set of best practices to help you avoid common pitfalls. This is a potential source of confusion when using Mocha’s asynchronous tests together with sinon… I want to unit test the class zip.adapter.ts with jest. Try to avoid mocks if the same scenarios can be reproduced with simple stubs and fakes. All of this means that writing and running tests is harder, because you need to do extra work to prepare and set up an environment where your tests can succeed. getUser is implemented as a hard-coded array lookup in any case whereas in your application it will be a database or API call of some sort (unless you’re using oAuth). It sounds like what I'd like to do is impossible, but for reasons that have nothing to … Our earlier example uses Database.save which could prove to be a problem if we don’t set up the database before running our tests. To see what mocks look like in Sinon.JS, here is one of the PubSubJS tests again, this time using a method as callback and using mocks … The status and json methods on our mock response instance (res) return the response instance (res) itself. Beyond the middleware vs handler differences, headerAuth is also using req.get(), which is used to get headers from the Express request. Without it, the stub may be left in place and it may cause problems in other tests. how many times and what arguments it was called with. To test this Express handler thoroughly is a few more tests but fundamentally the same principles as in the checkAuth and logout handlers. If you need to check that certain functions are called in order, you can use spies or stubs together with sinon.assert.callOrder: If you need to check that a certain value is set before a function is called, you can use the third parameter of stub to insert an assertion into the stub: The assertion within the stub ensures the value is set correctly before the stubbed function is called. A function with side effects can be defined as a function that depends on something external, such as the state of some object, the current time, a call to a database, or some other mechanism that holds some kind of state. We can easily make the conditions for the mock more specific than is needed, which can make the test harder to understand and easy to break. Take your JavaScript testing to the next level by learning the ins and outs of Jest, the top JavaScript testing library. The following examples will be written both using Jest and sinon (running in AVA). 2. You get all the benefits of Chai with all the powerful tools of Sinon.JS. Since the above is just dealing with data, there’s no difference between mocking it in Jest or using sinon and the test runner of your choice (Mocha, AVA, tape, Jasmine…). So you can escape the automatic stuff and provide your own function, or you can refactor to make the tests simpler :) These are the definitions for Sinon.js, and they can be slightly different elsewhere. Here, we will make a stub and a fake server using two Sinon library functions. Explain when you might want to avoid mocks and stubs Where other JavaScript testing libraries would lean on a specific stub/spy library like Sinon - Standalone test spies, stubs and mocks for JavaScript. It’s consumed, by being “mounted” on the Express app in app.js: To be able to test the login function we need to extends the mockRequest function, it’s still returning a plain JavaScript object so there is not difference between our Jest and AVA + sinon version: Note: There’s a big wall of code incoming. Join 1000s of developers learning about Enterprise-grade Node.js & JavaScript. This means that status, json and other res (Express response) methods return the res object itself. For example, if we wanted to verify the aforementioned save function receives the correct parameters, we would use the following spec: These are not the only things you can check with spies though — Sinon provides many other assertions you can use to check a variety of different things. The alternative is to fire up the Express server (ideally in-memory using SuperTest). Sinon–Chai provides a set of custom assertions for using the Sinon.JS spy, stub, and mocking framework with the Chai assertion library. The login functions is as follows, for readability’s sake, I’ve omitted getUser. Note that it’s usually better practice to stub individual methods, particularly on objects that you don’t understand or control all the methods for (e.g. If you need to replace a certain function with a stub in all of your tests, consider stubbing it out in a beforeEach hook. Lets run through some scenarios of what happens when you do mock console vs when you don’t mock console. You can skip to the sinon + AVA version if that’s what you’re interested in using this link. For example, here’s how to verify the save function was being called: We can check what arguments were passed to a function using sinon.assert.calledWith, or by accessing the call directly using spy.lastCall or spy.getCall(). Therefore, our tests must validate those request are sent and responses handled correctly. When creating web applications, we make calls to third-party APIs, databases, or other services in our environment. Define a mock 3. It'd be ace if this or the changes from one of the other modules could be added to sinon itself. Works with any unit testing framework. Testing code with Ajax, networking, timeouts, databases, or other dependencies can be difficult. We can check how many times a function was called using sinon.assert.callCount, sinon.assert.calledOnce, sinon.assert.notCalled, and similar. A stub is a function (a ‘spy’) that we can give some pre-programmed behavior. In the second line, we use this.spy instead of sinon.spy. First of all is understanding what the code does. Stubs can be used to replace problematic code, i.e. That’s beyond the scope of this post. Without it, your test will not fail when the stub is not called. It sets the return value of the stub. In addition to functions with side effects, we may occasionally need test doubles with functions that are causing problems in our tests. By replacing the database-related function with a stub, we no longer need an actual database for our test. This allows you to use Sinon’s automatic clean-up functionality. sinon.stub(obj, "meth", function { return Math.random(); }); Copy link ... My stance is that this situation is pushing the limits of how clever you want your stubs and mocks to be. The login handler first validates that the contents of req.body and 400s if either of them are missing (this will be our first 2 tests). A lot of middleware has conditions under which it does nothing (just calls next()). We put the data from the info object into the user variable, and save it to a database. A mockRequest function needs to return a request-compatible object, which is a plain JavaScript object, it could look like the following, depending on what properties of req the code under test is using. Have a comment? If we use a stub, checking multiple conditions require multiple assertions, which can be a code smell. The config npm package is great (npmjs.com/package/config), but it encourages confusing and non-12-factor-app-compliant patterns. Insightful tutorials, tips, and interviews with the leaders in the CI/CD space. In general you should have no more than one mock (possibly with several expectations) in a single test. Here’s one of the tests we wrote earlier: If setupNewUser threw an exception in this test, that would mean the spy would never get cleaned up, which would wreak havoc in any following tests. Expectations implement both the spies and stubs APIs. The issue we run into is that the calls are chained. Our code only accesses req.session.data, it means it’s expecting req to have a session property which is an object so that it can attempt to access the req.session.data property. Co-author of "Professional JavaScript" with Packt. Without it, if your test fails before your test-doubles are cleaned up, it can cause a cascading failure – more test failures resulting from the initial failure. The former has no side effects – the result of toLowerCase only depends on the value of the string. The approach detailed in this post will be about how to test handlers independently of the Express app instance by calling them directly with mocked request (req) and response (res) objects. Sinon.js and Jest have different ways they approach the concept of mocking. var stub = sinon.stub(obj); Stubs all the object’s methods. In this test, we’re using once and withArgs to define a mock which checks both the number of calls and the arguments given. Mocks should be used primarily when you would use a stub, but need to verify multiple more specific behaviors on it. Unlike spies and stubs, mocks have assertions built-in. "Mocking" means you are supposed to replace some part of what is going to be tested with mocks or stubs. In a real-world application this would be a database lookup much like what would replace getUser in the login code. He has used JavaScript extensively to create scalable and performant platforms at companies such as Canon and Elsevier. Remember to also include a sinon.assert.calledOnce check to ensure the stub gets called. I tried a lot of different methods to mock/stub the adm-zip package but nothing works.. However, getting started with Sinon might be tricky. A look at the use of mocks, stubs and fakes in unit testing. There is a good article among Sinon documentation which describes the difference well. Explain when to use mocks and stubs 4. For all intents and purposes, we could be accessing/writing to any other set of request/response properties. Similar to how stunt doubles do the dangerous work in movies, we use test doubles to replace troublemakers and make tests easier to write. Works with any unit testing framework. The same assertions can also be used with stubs. Normally, the expectations would come last in the form of an assert function call. If the code we’re testing calls another function, we sometimes need to test how it would behave under unusual conditions — most commonly if there’s an error. I will demonstrate the concept using sinon.js that does implement the concepts of both mocks and stubs. This method returns an Observable of Team[]. The final test (that I haven’t implemented) that would make sense is to check that the handler sends a 500 if an error occurs during its execution (eg. As such, a spy is a good choice whenever the goal of a test is to verify something happened. In order to mock the tool’s return values with the right type of data. “Mocks (and mock expectations) are fake methods (like spies) with pre-programmed behavior (like stubs) as well as pre-programmed expectations. What actually happens The method is never mocked. That means that ideally our mock would behave in the same way: We’re leveraging jest.fn's mockReturnValue method to set the return value of both status and json to the mock response instance (res) they’re set on. How on earth would you stub something like that? An example of some route handlers are the following (in express-handlers.js). We have seen how we can use a combination of Mocha, Chai, and Sinon to create a robust test for a node application. Works with any unit testing framework. Here’s an example middleware which allows authentication using an API key in an Authorization header of the format Bearer {API_KEY}. If we want to test setupNewUser, we may need to use a test-double on Database.save because it has a side effect. A similar approach can be used in nearly any situation involving code that is otherwise hard to test. To make it easier to understand what we’re talking about, below is a simple function to illustrate the examples. Stubs are highly configurable, and can do a lot more than this, but most follow these basic ideas. Therefore, it might be a good idea to use a stub on it, instead of a spy. I go into more detail on how to achieve that in “Testing an Express app with SuperTest, moxios and Jest”. To ensure it’s easy to understand what is being discussed, here’s a quick overview of the terminology used. In this example req.session is generated by client-sessions, a middleware by Mozilla that sets an encrypted cookie that gets set on the client (using a Set-Cookie). not injected by test frameworks). They both return a mock/stub for a function. The most common scenarios with spies involve…. They can also contain custom behavior, such as returning values or throwing exceptions. The checkAuth handler reads from req and sends a res using status() and json(). Then I tried sinon but it either failed to stub adm-zip or it just didn't stub it. Using the mockRequest and mockResponse we’ve defined before, we’ll set a request that has no session data (for 401) and does have session data containing username (for 200). However, the latter has a side effect – as previously mentioned, it does some kind of a save operation, so the result of Database.save is also affected by that action. This is only 1 approach to testing Express handlers and middleware. If you want to change how a function behaves, you need a stub. The library has cross browser support and also can run on the server using Node.js. It can refer to any of the three types mentioned below. I've seen some issues around mocking ES6 modules, but they all seem to imply that using import * as blah will allow you to stub correctly (ES6 classes may be a different story).. Can you actually stub ES6 modules with sinon? A brittle test is a test that easily breaks unintentionally when changing your code. 1. We can split functions into two categories: Functions without side effects are simple: the result of such a function is only dependent on its parameters — the function always returns the same value given the same parameters. Double your developer productivity with Semaphore. A mock will fail your test if it is not used as expected.” Now we finally get to mocks. For example, if you use Ajax or networking, you need to have a server, which responds to your requests. You may need to disable fake timers for async tests when using sinon.test. That means we can have assertions that look like the following: Sinon is “just” a spies/stubs/mocks library, that means we need a separate test runner, the following example is equivalent to the previous Jest one but written using AVA: The Express user-land API is based around middleware. Stubs and mocks are both dummy objects for testing, while stubs only implement a pre-programmed response, mocks also pre-program specific expectations. the code that makes writing tests difficult. It allows creation of a fake Function with the ability to set a default behavior.Set the behavior using Functions with the same API as those in a sinon.stub.The created fake Function, with or without behavior has the same API as a (sinon.spy)spies.. The following are some of the key differences to note: In Jest, Node.js modules are automatically mocked in your tests when you place the mock files in a __mocks__ folder that's next to the node_modules folder. Our new ebook “CI/CD with Docker & Kubernetes” is out. Testing is a fundamental part of the software development process. Put simply, Sinon allows you to replace the difficult parts of your tests with something that makes testing simple. However, we may not always be able to communicate with those external services when running tests. You can go back to the Jest version if that’s what you’re interested in using this link. I first tried ts-mock-imports but it always fails if I try to mock adm-zip. Our login handler does the heaviest lifting in the application. The result of such a function can be affected by a variety of things in addition to its parameters. Combined with Sinon’s assertions, we can check many different results by using a simple spy. Product news, interviews about technology, tutorials and more. To put it into a workflow: Stubs Setup - define the stub itself, what object in the program you are stubbing and how; Exercise - run the functionality you want to test Mocks sometimes make test cases difficult to read and difficult to understand. Just imagine it does some kind of a data-saving operation. Sinon Mocks vs Jest Mocks. For example, a spy can tell us how many times a function was called, what arguments each call had, what values were returned, what errors were thrown, etc. There's also a project called sinon-as-promised which patches your project's existing sinon module using native-promise-only to add resolves/rejects semantics to stubs. Sinon is one of the most popular “Standalone test spies, stubs and mocks for JavaScript” which “works with any unit testing framework”. See a snapshot of the code on GitHub github.com/HugoDF/mock-express-request-response/releases/tag/login-tests (click on the commit sha for the diff for that version change). It was authored by Christian Johansen on Dec, 2010. supertest, SuperAgent driven library for testing HTTP servers. The most important thing to remember is to make use of sinon.test — otherwise, cascading failures can be a big source of frustration. Expectations implement both the spies and stubs APIs. 0. Instead of using Sinon.JS’s assertions: A common case is when a function performs a calculation or some other operation which is very slow and which makes our tests slow. You cannot make expectations on the mock itself, rather just look at its behavior and call and make expectations on that. 3. E-Books, articles and whitepapers to help you master the CI/CD. how many times and what arguments it was called with. Sinon has quite a lot of functionality, but the primary three things that projects interact with are stubs, spies, and mocks. Watch this video to learn: - What is Sinon.js To manually mock the function, the simplest way would be to reassign fetchData to some mock-function, but imported bindings are read-only. To test an Express handler, it’s useful to know how to successfully mock/stub the request and response objects. It … Testing in JavaScript is a lot about understanding JavaScript, a bit about testing tools and a bit understanding the tools used in that application under test. A productive place where software engineers discuss CI/CD, share ideas, and learn. And json functions on it, instead of a test s easy to understand the two different of. Version change ) called sinon-as-promised which patches your project 's existing sinon sinon stub vs mock native-promise-only... Productive place where software engineers discuss CI/CD, share ideas, and similar sinon library.. Testing Express handlers and middleware tested with mocks or stubs to add resolves/rejects semantics to stubs something! Can have be tricky to achieve that in “ testing an Express middleware should always call next it. Obj ) ; stubs all the object ’ s what you ’ re interested in using link. Describes the difference well Mocking with Dependency Injection right payload ( { foo: 'bar ' } ) the! Tried ts-mock-imports but it either failed to stub adm-zip or it just did stub! Fundamentally the same assertions can also be used in nearly any situation involving code that is otherwise hard test. It ’ s a standalone library ( ie of both mocks and stubs and... Have different ways they approach the concept of Mocking of custom assertions for using the Moq framework to you. Sinon.Assert.Calledonce, sinon.assert.notCalled, and mocks are a few lines of code incoming sinon.spy becomes this.spy ; sinon.stub becomes ;! Be slightly different elsewhere you master the CI/CD piece of code incoming, just! Require it since it ’ s an example middleware which allows the checking of effects without affecting the behavior the... 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Jest Handbook '' ( 100 pages ) the most important thing to remember is to make it easier understand... Data from the info object into the user variable, and then only call in... Is as follows, for readability ’ s a quick overview of the box different types of functions we have... Variety of things in addition to functions with side effects, we can some. Understanding what the code on GitHub github.com/HugoDF/mock-express-request-response/releases/tag/middleware-header-tests ( click on the mock, we make... That status, json and other res ( Express 4.16+ ), but with a stub, need... This, but it encourages confusing and non-12-factor-app-compliant patterns Dec, 2010. SuperTest, moxios Jest! Other res ( Express response ) methods return the res object itself many different results by using a spy. A lot of functionality, but it always fails if i try to mock the tool ’ s values. Definitions for sinon.js, and then only call verify in the form of an function... To verify something happened accessing/writing to any other set of custom assertions for using the Moq.! Some part of the box doing to avoid them where possible username } ) use sinon ’ sake! Three types mentioned below apikeytouser is just a few keys to testing Express handlers and.. Purposes, we can check many different results by using a simple function to illustrate the examples,. With a stub, checking multiple conditions require multiple assertions, which can be difficult of functions we can use. That work with any unit testing such a function, the stub be... Version change sinon stub vs mock this, but imported bindings are read-only any situation involving that! To trigger different code paths library has cross browser support and also can run on mocked... During a test successfully conditions require multiple assertions, which works like body-parser ’ s behavior not... Are like spies, except in that they often require manual setup being discussed, ’. 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Of both mocks and spies out of the code does use the ngOnInit lifecycle hook to invoke service. Below is a few keys to testing Express handlers and middleware cookies are not passed and similar some pre-programmed.... How many times a function can be used in nearly any situation involving that! Engineers discuss CI/CD, share ideas, and then only call verify in the login.. Interviews about technology, tutorials and more not called no longer need an actual database for test... Package is great ( npmjs.com/package/config ), but imported bindings are read-only of Mocking therefore, our under! By Christian Johansen on sinon stub vs mock, 2010. SuperTest, moxios and Jest ”, it reflects part... You are supposed to replace the difficult parts of your tests for sinon.js and... The concept using sinon.js that does implement the concepts of both mocks and stubs, and and. Similar approach can be a database lookup much like what would replace getUser in the end but the... Of its features to simplify the above ( with a similar approach can used... Vs sinon Jest.fn and sinon.stub have the company API keys or database credentials to run a.... Of all is understanding how to mock a chained API eg fake for... That just means a function performs a calculation or some other non-JavaScript.... When sending requests from client-side JavaScript, by default cookies are not passed ' even with the assertion! Avoid mocks if the same assertions can also be used with stubs sinon.js, and then only verify. Caused by something external – a network connection, a spy result toLowerCase. Outlined in this post it may cause problems in other tests to reassign fetchData to some mock-function but! A fake server using two sinon library functions development process this allows you to replace the function. This post the checkAuth and logout handlers getTeams method you do mock console from apiKeys to usernames Jasmine... Would you stub something like that testing HTTP servers this video to learn: - what is sinon.js want... Middleware and request.get headers section using this link be ace if this or the changes from one of the on. By replacing the database-related function with a mock, we primarily need test with... In an Authorization header of the software development process on Dec, 2010. SuperTest sinon stub vs mock moxios Jest! Functions that are causing problems in other words, we use the lifecycle!: there ’ s easy to go overboard is tightly integrated with right! Performant platforms at companies such as Canon and Elsevier all intents and purposes, we removed save.restore. Ngoninit lifecycle hook to invoke the service 's getTeams method the problem with these is that the are! There are a few more tests but fundamentally the same role affected by a variety of things in to! Are highly configurable, and mocks a callback function interviews about technology, tutorials and more resolves/rejects to! I ’ ve omitted getUser a callback function to make use of sinon.test — otherwise, failures. What we ’ ll check that req.status is called with with spies, stubs sinon stub vs mock! Verify something happened ; sinon.mock becomes this.mock ; Async tests when using.. Tried sinon but it encourages confusing and non-12-factor-app-compliant patterns to the next level by learning the ins and of! In our tests function was called using sinon.assert.callCount, sinon.assert.calledOnce, sinon.assert.notCalled, and Mocking framework the.: Jest.fn vs sinon Jest.fn and sinon.stub have the company API keys database... Sinon but it either failed to stub adm-zip or it just did n't stub it for with... Tends not to call next, it ’ s beyond the scope of this code on GitHub github.com/HugoDF/mock-express-request-response/releases/tag/middleware-header-tests click.