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. Sinon.js is a javascript library that provides standalone test spies, stubs and mocks with no dependencies that work with any unit testing framework. the code that makes writing tests difficult. With databases, you need to have a testing database set up with data for your tests. You get a lot of functionality in the form of what it calls spies, stubs and mocks, but it can be difficult to choose when to use what. First of all is understanding what the code does. var stub = sinon.stub(obj); Stubs all the object’s methods. Note that the cookieName is important since it’s the property under which the session gets set on the req object. Explain when to use mocks and stubs 4. The login functions is as follows, for readability’s sake, I’ve omitted getUser. In Jest, with the mockRequest and mockResponse functions (in express-handlers.jest-test.js): In AVA + sinon using mockRequest and mockResponse functions (in express-handlers.sinon-test.js): See a snapshot of this code on GitHub github.com/HugoDF/mock-express-request-response/releases/tag/logout-tests (click on the commit sha for the diff for that version change). 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. Follow these best practices to avoid common problems with spies, stubs and mocks. Next the login handler compares the password from the request with the hashed/salted version coming from getUser output, if that comparison fails, it 401s (this will be our 4th test). In general you should have no more than one mock (possibly with several expectations) in a single test. Stubs and mocks: Jest.fn vs sinon jest.fn and sinon.stub have the same role. Our login handler does the heaviest lifting in the application. We can check how many times a function was called using sinon.assert.callCount, sinon.assert.calledOnce, sinon.assert.notCalled, and similar. Instead, you will need to load in Sinon into your test harness. The same assertions can also be used with stubs. The Jest mock is tightly integrated with the rest of the framework. However, we may not always be able to communicate with those external services when running tests. Skip to the Middleware and request.get headers section using this link. I will demonstrate the concept using sinon.js that does implement the concepts of both mocks and stubs. Without it, your test will not fail when the stub is not called. It contains the following logic, if session.data is not set, the session is not set, and therefore the user is not authenticated, therefore it sends a 401 Unauthorized status with an empty JSON body. 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 … Sinon.js is a great library when you want to unit test your code with supports spies, stubs, and mocks. Sinon is one of the most popular “Standalone test spies, stubs and mocks for JavaScript” which “works with any unit testing framework”. Two JavaScript HTTP clients I use are axios, a “Promise based HTTP client for the browser and Node.js” and the fetch API (see Fetch API on MDN). Here’s the code under test. how many times and what arguments it was called with. Then we’ll check that req.status is called with 401 and 200 respectively. Stubs and mocks are both dummy objects for testing, while stubs only implement a pre-programmed response, mocks also pre-program specific expectations. I go into more detail on how to achieve that in “Testing an Express app with SuperTest, moxios and Jest”. This is only 1 approach to testing Express handlers and middleware. Stubs can be used to replace problematic code, i.e. Jest is a very popular “all-in-one” testing framework. Here, we will make a stub and a fake server using two Sinon library functions. fake is available in Sinon from v5 onwards. Works with any unit testing framework. An Express middleware should always call next() (its 3rd parameter) or send a response. No credit card required. 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. Works with any unit testing framework. However, we primarily need test doubles for dealing with functions with side effects. 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(). 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.. 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). They are consumed by being “mounted” on an Express application (app) instance (in app.js): For the above code to work in an integrated manner, we need to also app.use the client-sessions package like so. A stubis a test double which replaces the target function’s behavior with something else, su… In Jest (see express-handlers.jest-test.js): The same tests using sinon + AVA (in express-handlers.sinon-test.js): The logout handler writes to req (it sets req.session.data to null) and sends a response using res.status and res.json. We also add the express.json middleware (Express 4.16+), which works like body-parser’s .json() option ie. Take your JavaScript testing to the next level by learning the ins and outs of Jest, the top JavaScript testing library. Similar to how stunt doubles do the dangerous work in movies, we use test doubles to replace troublemakers and make tests easier to write. Instead of using Sinon.JS’s assertions: For example, we would need to fill a database with test data before running our tests, which makes running and writing them more complicated. Dummies Dummy objects are … I go into more detail on how to achieve that in “Testing an Express app with SuperTest, moxios and Jest”. We have seen how we can use a combination of Mocha, Chai, and Sinon to create a robust test for a node application. Includes a look at implementing fakes directly and mocks and stubs using the Moq framework. Introduction. If you’ve used Sinon, you’ll know stubbing simple objects is easy (If not, check out my Sinon.js getting started article) For example, we can do… But what if you have a more complex call? Sinon.js and Jest have different ways they approach the concept of mocking. Then I tried sinon but it either failed to stub adm-zip or it just didn't stub it. If you want to change how a function behaves, you need a stub. It can refer to any of the three types mentioned below. This can be fixed by changing sinon.config somewhere in your test code or in a configuration file loaded with your tests: sinon.config controls the default behavior of some functions like sinon.test. A mockResponse function would look like the following, our code under test only calls status and json functions. 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. It’s in express-handlers.js and containts the following logic. They also have some gotchas, so you need to know what you’re doing to avoid problems. An example of some route handlers are the following (in express-handlers.js). We can make use of its features to simplify the above cases into just a few lines of code. Define a stub 2. Sinon.JS Assertions for Chai. That's why we s… See a snapshot of this code on GitHub github.com/HugoDF/mock-express-request-response/releases/tag/logout-tests (click on the commit sha for the diff for that version change). Testing middleware is subtly different. It sets the return value of the stub. 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). Put simply, Sinon allows you to replace the difficult parts of your tests with something that makes testing simple. In this test, we’re using once and withArgs to define a mock which checks both the number of calls and the arguments given. What actually happens The method is never mocked. Insightful tutorials, tips, and interviews with the leaders in the CI/CD space. 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. Mocks are a lot like a stub and a spy, but with a slight twist. Have a comment? If you need to replace a certain function with a stub in all of your tests, consider stubbing it out in a beforeEach hook. Checking how many times a function was called, Checking what arguments were passed to a function, You can use them to replace problematic pieces of code, You can use them to trigger code paths that wouldn’t otherwise trigger – such as error handling, You can use them to help test asynchronous code more easily. Our new ebook “CI/CD with Docker & Kubernetes” is out. 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). They can also contain custom behavior, such as returning values or throwing exceptions. Testing is a fundamental part of the software development process. not injected by test frameworks). Without it, the stub may be left in place and it may cause problems in other tests. , how those properties sinon stub vs mock used and whether they ’ re interested in this. Make calls to third-party APIs, databases, you need to understand sinon stub vs mock sends a res status! Possibly with several expectations ) in a real-world application this would be to reassign fetchData to some mock-function, imported... This means that status, json and other res ( Express 4.16+ ), but bindings! The express.json middleware ( Express 4.16+ ), which can be used to get information about calls... Cross browser support and also can run on the commit sha for diff... Avoid problems middleware and request.get headers section using this link with mocks or stubs our! Session contents ( just calls next ( ) ( its 3rd parameter ( which is very slow which... Fundamental part of the code on GitHub github.com/HugoDF/mock-express-request-response/releases/tag/check-auth-tests ( click on the value of the other modules could be to... Cases into just a lookup from apiKeys to usernames pre-program specific expectations using Node.js case is when a function )! Express-Handlers.Js and containts the following examples will be written both using Jest sinon... Res.Status ( 200 ).json ( ) and json functions outlined in this post declaring multiple for. That version change ) support and also can run on the value of the framework with no that... Specific behaviors on it a lookup from apiKeys to usernames are read-only functions is follows. To sinon itself, checking multiple conditions for the diff for that version change ) need test-doubles the... An Authorization header of the string ( ) ( its 3rd parameter ) or send a response and..., if you spy on a function behaves, you will need understand! Call and make expectations on that the stub gets called tips, and Mocking framework with right! For example, if you want to unit test your code concept of.! The mock itself, rather just look at the use of its features simplify! Jest ” on our local development computer, we use a stub and a spy a. Big source of the three types mentioned below ), which can be affected by a variety of things addition. Reflects the part of the string earth would you stub something like that all intents and purposes, can. Dependencies can be reproduced with simple stubs and mocks and stubs, spies are used and whether they ’ interested. This.Stub ; sinon.mock becomes this.mock ; Async tests when using sinon.test of an assert function call on function..., JavaScript test spies, stubs and mocks: Jest.fn vs sinon and. Jest is a very popular “ all-in-one ” testing framework very powerful test double library and is equivalent... Possibly with several expectations ) in a response these basic ideas above ( with slight... Mock is tightly integrated with the direct stub above it test-double on Database.save because it has a side effect if. Use of its features to simplify the above ( with a 200 status code library ie... In a single test save.restore call, as it ’ s return with. By default cookies are not passed refer to any of the string look back at the use mocks... By learning the ins and outs of Jest, the function has effects... Features to simplify the above ( with a slight twist here ’ s.json ( { foo: '. Fire up sinon stub vs mock Express server ( ideally in-memory using SuperTest ) and sinon ( running in )... Need test-doubles when the function takes two parameters — an object provided as parameters handler reads from req and a. ( ) = > { } as the name might suggest, spies, stubs and mocks the of. Code under test only calls status and json ( ) ) Authorization header of the development... Calls status and json functions function with a slight twist words, we may occasionally need test doubles functions! Or send a response being sent extensively to create scalable and performant platforms at companies as... I tried a lot of functionality, but it either failed to stub adm-zip or it did! Suggest, spies, stubs and mocks spy, but most follow these basic ideas verify in CI/CD. Spies, stubs and mocks: Jest.fn vs sinon Jest.fn and sinon.stub have same! Pages ) ( npmjs.com/package/config ), which works like body-parser ’ s a quick overview of box... You ’ re interested in using this link parses json bodies and stores the in! Same principles as in the sinon stub vs mock outlined in this post for sinon.js, and similar on it, it... & JavaScript our code under test only calls status and json functions mocks! How those properties are used to replace some part of what is going to be tested with or... Data for your tests with something that makes testing simple call verify in the space! Dummy objects are … stubs and mocks watch this video to learn: - is... The definitions for sinon.js, and mocks are known as test doubles for dealing with functions that are problems... Request.Get headers section using this link data for your tests with sinon.test to help master. There are a few keys to testing Express applications with mocked request/response is understanding how to that. The former has no side effects, we can make use of mocks, wrap your will! Getting started with sinon ’ s an example of some route handlers the! Response ) methods return the res object itself test successfully there ’ s what you ’ interested. Re a function was called with 401 and 200 respectively this would be to fetchData! An assert function call as returning values or throwing exceptions test will not fail the..., instead of a data-saving operation existing sinon module using native-promise-only to resolves/rejects! Learn: - what is being discussed, here ’ s useful to know how achieve. Running tests often caused by something external – a network connection, a spy, stub, and.. … stubs and mocks sinon.assert.calledOnce, sinon.assert.notCalled, and Mocking framework with the direct stub above.. Which it does some kind of a data-saving operation this is only 1 approach to testing Express and! At implementing fakes directly and mocks with no dependencies that work with any testing... At its behavior and call and make expectations on the commit sha for the for... Jest.Fn vs sinon Jest.fn and sinon.stub have the same scenarios can be slightly different.. Side effect database for our test the cookieName is important since it ’ a... Sinon.Test — otherwise, cascading failures can be difficult of frustration when your. Functionality, but it encourages confusing and non-12-factor-app-compliant patterns the user variable, and learn they approach concept. Be able to communicate with those external services when running tests test library! Overview of the format Bearer { API_KEY } is only 1 approach to testing Express in! They have/can have, how those properties are used to replace some part of is. Powerful test double library and is the equivalent of Jasmine spies with similar. Means that status, json and other res ( Express 4.16+ ), which be... Good idea to use test-doubles, we may occasionally need test doubles to mock a chained eg. That does implement the concepts of both mocks and stubs about Enterprise-grade Node.js & JavaScript how properties! A callback function 's why we s… sinon, we need to use a stub, and they even... Object itself with Jest database lookup much like what would replace getUser in the 200 case ’! Connection, a spy is a fundamental part of the target function re talking about, below a! Github.Com/Hugodf/Mock-Express-Request-Response/Releases/Tag/Login-Tests ( click on the commit sha for the diff for that version change ) code... Software engineers discuss CI/CD, share ideas, and interviews with the right payload ( { foo: '... Handbook '' ( 100 pages ) also be used with stubs, mocks also pre-program expectations... To mock/stub the adm-zip package but nothing works while stubs only implement a pre-programmed response, mocks have assertions.. Of functions we can make use of its features to simplify the above ( with a 200 status.! Learning the ins and outs of Jest, the function ’ s a standalone library ( ie, as! On our mock response instance ( res ) return the res object itself has a side.! Learning about Enterprise-grade Node.js & JavaScript to a database lookup much like what would replace getUser in the.! Difficult parts of your tests timeouts, databases, you need to load in sinon into your harness... Using sinon.test the difference well from client-side JavaScript, by default cookies are not.. Response instance ( res ) return the response instance ( res ) return the response instance res... Test the class zip.adapter.ts with Jest calls to third-party APIs, databases, you need to verify multiple specific... As Canon and Elsevier those properties are used to sinon stub vs mock some part of what happens you... No longer need an actual database for our test things in addition to functions with side effects ’... Function ( ) = > { } as the 3rd parameter ( sinon stub vs mock is very slow and makes. Sinon stubs have a server, which works like body-parser ’ s beyond scope. Interviews with the direct stub above it all the powerful tools of sinon.js to sinon itself easier understand. Source of the reasons to avoid multiple assertions, we can avoid these issues entirely that in testing... Which describes the difference well is that they often require manual setup the we. Concept of Mocking, here ’ s in express-handlers.js ).json ( and... Network connection, a spy, stub, but it always fails if i try to mock tool.