Promises are becoming a common part of the JavaScript code. The native Promise object is already supported by all the major browsers including Chrome, Firefox, and Safari. Despite making asynchronous code simpler, dealing with promises in unit tests is a hassle.

jasmine test promise resolve

When you first encounter promises in unit tests, your test probably looks something like a typical unit test:. But then, the promise shows up, and the code gets complicated. The first one is for a resolved promise, which has an assertion inside it to compare equality, while the second one is for a rejected promise, which has a failing assertion.

We also need the done calls in both of them. Since promises are asynchronous, we must tell Mocha this is an asynchronous test, and notify it when done.

Testing promises with Jasmine

But why do we need assert. The purpose of this test is to compare the result of a successful promise against a value. If the promise is rejected, the test should fail.

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For instance, imagine we remove the rejection callback. Your code should look like this:. In this case, if the promise was rejected, there would be no error, since there is no error handler in the test to check for it. This is definitely one of the main reasons why promises become complicated in tests. I decided to use Mocha in this project because it has a built-in support for promises.

This means that a rejected promise will make your test fail. For example:. The above test returns a rejected promise, which means that it fails every time. The test now returns the promise.

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If the promise fails, Mocha will fail the test. With chai-as-promisedwe can! The key here is eventually. When comparing values with Chai, we can use. For example, with deep. The same warning applies here as without promises. Using eventually. You can use it for most equality comparisons with promises — with strings, numbers and so on — unless you specifically need a reference comparison.

Sometimes you might want to check against only a single property in an object from a promise. We can make use of the fact you can chain promises:. As the final alternative, if you are using ECMAScriptyou can make it a little bit cleaner using the fat arrow function syntax:. If you have multiple promises in tests, you can use Promise. But keep in mind that this is similar to having multiple assertions in a single test, which can be seen as a code smell. If you have two or more promises which you need to compare, then the following pattern can be used:.

Unit testing JavaScript with Promises and Jasmine

In other words, we can use all to resolve both promises, and use a function in then to run a normal Chai assertion on the returned values. Occasionally you might want to check that a certain call makes a promise fail instead of succeed. If you want to ensure the rejection comes with a specific type of error or message, you can also use rejectedWith :.It's common in JavaScript for code to run asynchronously.

When you have code that runs asynchronously, Jest needs to know when the code it is testing has completed, before it can move on to another test. Jest has several ways to handle this. For example, let's say that you have a fetchData callback function that fetches some data and calls callback data when it is complete.

You want to test that this returned data is the string 'peanut butter'. By default, Jest tests complete once they reach the end of their execution. That means this test will not work as intended:.

The problem is that the test will complete as soon as fetchData completes, before ever calling the callback. There is an alternate form of test that fixes this. Instead of putting the test in a function with an empty argument, use a single argument called done. Jest will wait until the done callback is called before finishing the test.

If done is never called, the test will fail with timeout errorwhich is what you want to happen. If the expect statement fails, it throws an error and done is not called. If we want to see in the test log why it failed, we have to wrap expect in a try block and pass the error in the catch block to done. Otherwise, we end up with an opaque timeout error that doesn't show what value was received by expect data. If your code uses promises, there is a more straightforward way to handle asynchronous tests.

Return a promise from your test, and Jest will wait for that promise to resolve. If the promise is rejected, the test will automatically fail. For example, let's say that fetchDatainstead of using a callback, returns a promise that is supposed to resolve to the string 'peanut butter'. We could test it with:. Be sure to return the promise - if you omit this return statement, your test will complete before the promise returned from fetchData resolves and then has a chance to execute the callback.

EP 13.7 - Angular / Unit Testing / Asynchronous Code

If you expect a promise to be rejected, use the. Make sure to add expect. Otherwise a fulfilled promise would not fail the test. You can also use the. Be sure to return the assertion—if you omit this return statement, your test will complete before the promise returned from fetchData is resolved and then has a chance to execute the callback.

It works analogically to the. If the promise is fulfilled, the test will automatically fail. Alternatively, you can use async and await in your tests. To write an async test, use the async keyword in front of the function passed to test. For example, the same fetchData scenario can be tested with:. You can combine async and await with.

In these cases, async and await are effectively syntactic sugar for the same logic as the promises example uses. None of these forms is particularly superior to the others, and you can mix and match them across a codebase or even in a single file. It just depends on which style you feel makes your tests simpler. Callbacks The most common asynchronous pattern is callbacks.

Promises If your code uses promises, there is a more straightforward way to handle asynchronous tests.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time.

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I try to test my app with Jasmine and got the following problem: I will calculate something in the then function of my promise.

That's the point where I need to test my code. So how could I test the code inside the then function? Thanks for help. Jasmine's default timeout is 5 seconds per test, so if the async stuff isn't done by then jasmine will crash. You can change this setting in the configs or set it in the terminal. I think that if it doesn't work in 10 seconds, you may have faulty methods. This stuff should only take this long if you are performing HEAVY computations, or are hitting an external api with a not-so-great internet connection.

One approach I've found useful when testing is mocking dependencies. I've tried to comment out what I've done as much as possible. Official Jasmine Docs explain most of the concepts extensively. Hope the solution helps!!!! Let me tell ya what I do, for Angular 1. In angular 1.

jasmine test promise resolve

In angular 2. From the Angular 1. The disadvantage is that your code is tied to angular, the advantages are that your code is flat and it's portable to 2. I was a fan of the mocha test runner that allowed me to return promises in my tests, you could try to get that going, but there are downsides to that as well like needing to modify your code specifically for a test. Not after it, or before it. But inside it. Learn more.Testing synchronous specs is easy, but asynchronous testing requires some additional work.

For example, the code below fails because Jasmine evaluates the expect piece before the testAsync function has finished its work. The setTimeout call forces a two second delay, but Jasmine has already moved on and failed the test before the setTimeout completes:. With Jasmine async testing, we have to call the async code in the beforeEach function that runs before each it function block within a describe function block.

We also have to let Jasmine know when the async function has completed by calling the special done callback function Jasmine provides. Here, we are passing this special done callback around so our code under test can invoke it. This works, but changing the code under test to accept the done callback argument and invoke it may not be realistic.

Why would you change your code under test just to make the testing framework happy? Instead, you can use promises and call the special Jasmine done callback when your promise has resolved. Note that the Jasmine done callback is NOT the same as the promise's done callback. They just use the same function name. Deferred object for the promises, but this approach should work with any promises library.

jasmine test promise resolve

You can even use the data returned from the promise in the test once it is resolved. Here we are passing the return value in the deferred. We use cookies make this site better. Privacy Policy. The setTimeout call forces a two second delay, but Jasmine has already moved on and failed the test before the setTimeout completes: With Jasmine async testing, we have to call the async code in the beforeEach function that runs before each it function block within a describe function block.

Cookie Policy We use cookies make this site better. Privacy Policy Accept.I wrote a mock-promises to address it. A recent project of mine included a single page Marionette app that used promises around the requests for model data. Promises are a useful alternative to callbacks and events.

More detailed explanations can be found here or here. If you have lots of event binding in your code, I suggest you give them a look. In the course of my app, I might write some function addModelFromPromise that looks something like. If you wanted to test addModelFromPromiseyou could imagine writing a Jasmine test for like.

This test feels like it would pass, but the callback to the promise is asynchronous, and it will not be called until the synchronous JavaScript ie your testis finished. To solve this in Jasmine 2, you need to use the done callback. This works well enough, but at some cost. For starters, it is harder to read. Also, What happens if you did the done wrong and the expect is never called?

Now you want to write some extra code to check on this. Keep in mind, this is testing an extremely simple function, if you have more than one promise, or nested promises, or any other source of asynchrony, the tests require a tangle of callbacks before you can get to an expect.

To solve this problem, I wrote a promise mocking framework, mock-promises. The interface was inspired by jasmine-ajax and the development was done on Jasmine, but it does not require Jasmine. The executeForPromise function synchronously executes all attached callbacks for that promise. When there are multiple promises, there is no nesting within nesting, only an extra executeForPromise.

It may not look like it, but I am pretty sure this is the best way to write this test. The first thing that stands out is the deeply nested callbacks. I had to use four anonymous functions just to get to my expect. The setTimeouts are even worse. Nothing like nested setTimeouts to feel confidence in your code execution order. This may look pretty bad, but I did end up needing to write things like this in my last project. The first time I wrote this test, it was twice as long and flaky.

The analogous mock-promises spec is:. The nested promises do require promises to be flushed twice, but otherwise, the test is now much more straightforward. There are some alternatives to mock-promises. You can mock the clock in jasmine and tick forward. This is will flush any resolved promises. Unfortunately, this does not work with native Promises.

It should be possible with the other promise libraries, but sometimes requires mocking the clock before you load the library. In a similar way, you can flush the scope in Angular. This type of alternative is not as clear as resolving an individual promise, but is lighter on the mocking side.

Unit Testing with $q Promises in AngularJS

As far as I can tell, the most popular mocking alternative is Jasmine-As-Promised. It does not support Jasmine 2. I am no longer on a project that requires promises, but the promise testing challenge is still fun.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. Minimal example demonstrating the problem. Since Angular uses mocks, pretty much everything has to be flushed by hand. Most of the AngularFire tests do something like this:. I think that was just a mistake.

This is not an angularFire issue. This requires all your promises to contain only synchronous code all the way up. You have to explicitly go around Angular and sleep the test and assume Firebase will fire the callback in that time.

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You're seeing totally different behavior in an app because your inside a digest cycle and your callbacks will be called upon promise resolution. You don't have a digest cycle in your tests. Here are some more interesting discussions about promises in Angular and alternatives for resolving them:. Challenge here is that there's no means of knowing when the Firebase call resolves to do the eval.

I guess you could get super hacky and attach an event listener that fires the loop. If the done method is located in the callback, there's no worry that it won't be called and the test could somehow pass. If you want to avoid using callbacks or listeners, that's the purview of a good mock tool, I think. The issue is getting a callback when the Firebase data returns.

jasmine test promise resolve

The promise handlers need to be flushed manually under test and you need to know when to flush. My example above just waits to do that. Another options would be to attach a listener directly to the reference itself and flush when there's data.

Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. New issue. Jump to bottom. Copy link Quote reply. This comment has been minimized. Sign in to view. That code expects me to be using callbacks - this issue is about promises. That still doesn't help - check out my repo. That's not how my tests are structured.

Sorry, didn't look at the example the first time. Assumed you were mocking FB. Thanks guys. This helped my understanding a lot. Looks like I've got some hackarounds to code.When developing unit tests in an angularJS app, you eventually stumble about a problem that can be quite frustrating to handle it in a clean und concisive way: promises. Clearly, you should mock someService, thats easy. But what to do with the promise? In my first couple of tests, I tried to reimplement promises somewhat and ended with ugly constructs like this:.

Of course, you can and maybe should be resolve the promise in the test itself if the data is different when you have more than one test. The catch is though, that you need to call rootScope.

After this method is finished, all promises are really resolved and you can test for the expected outcome. Maybe you want to try it without that call. I see no reason not work. Nice article though! I would expect the resolve to be enought but I guess it need that to process that assignment inside then success callback. I have a problem on how to use jasmine spy objects to test controllers that depends on a service and I have been tussling with this issue for some time now as I am quite new to AngularJS based developments.

While searching for a possible fix I stumbled on your article and attempted to implement test strategy suggested in your article but ran into further issues. Could you please suggest what changes should be made in order to implement this test correctly? In this controller I am trying to test the user login process and it calls loginRequest method in WebService to send out user credentials as a login message.

A login success message is received by the controller. If the login process is successful a URL redirection should happen. I have tried to use jasmine spy objects to mock the WebService functionality but I seem to be doing something wrong which I have been unable to pinpoint. But I am currently having a problem evaluating the received message status and evaluating the URL redirection process based on that.

Error ——- Chrome Instead you seem to ignore the return value to WebService. My example was specifically for unit testing when the service method is returning an angular promise when you call a then method on the return value of a service method call. You can find plenty of jsfiddle examples for this problem now, f.

Thank you for point out my mistake.

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Your points were helpful in fixing the problem. I managed to achieve this by testing the Broadcast event.