How my code behaves when the policy throws an exception, such as TimeoutRejectionException, BulkheadRejectedException or BrokenCircuitException. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, C# Kafka: How to Create a NetworkException Error, Unit testing internal methods in VS2017 .NET Standard library, Using Polly to retry on different Urls after failing retries. public void PassingTest () {. In your production code, inject the real policy you want to use. With HTTP requests, its not a question of if youll run into transient errors, but when. Thanks for your suggestions. Therefore it makes sense to be prepared and implement retry logic. If I configure Policy.Handle().Retry(3), it would be nice to check it really works, right? Right-click on the test project node in Solution Explorer for a pop-up menu. using xunit and moq. For Google Test documentation, see Google Test primer. Did the drapes in old theatres actually say "ASBESTOS" on them? Here are the scenarios I test for - How my code behaves when the policy throws an exception, such as TimeoutRejectionException, BulkheadRejectedException or BrokenCircuitException. In this blog I will try to explain how one can create clean and effective policies to retry API calls and have fallbacks when requests are failing. It will break when the configured number of exceptions have been thrown. For more information, see To link the tests to the object or library files. Install nuget Microsoft.Extensions.Http.Polly. The following table shows the calculated delay ranges using the formula above: Note: The reason it needs a lock when calling Random.Next() is because Random isnt threadsafe. Writing unit-tests to verify that Polly works can be a very valuable way to explore and understand what Polly does. If you check the constructor of HttpClient you will see that it inherits and abstract class IHttpMessageHandler which can be mocked since it is an abstract class. The text was updated successfully, but these errors were encountered: WebApplicationFactory.CreateClient() has no overloads that returns the named HttpClient: That makes sense: the Httpclient returned by WebApplicationFactory.CreateClient() is specifically geared to pass requests to your app from outside; the HttpClient instances configured within your app are (on the other hand) an internal concern to it. But, to allow you to concentrate on delivering your business value rather than reinventing Polly's test wheel, keep in mind that the Polly codebase tests its own operation extensively. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Why do men's bikes have high bars where you can hit your testicles while women's bikes have the bar much lower? Can be useful as a specification for, and regression check on, the faults you intend to handle. I cannot retrieve the HttpClient that has been configured with the Polly polly. Choose Add > Reference. An application can combine these two patterns. I want to add a delay when I receive a timeout. I hope you did learn something here. This will add quite a few extra scenarios where things can go wrong, the most commonly be timeouts and expiration of tokens. What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond? You would use Mountebank or HttpClientInterception to stub the outbound call from HttpClientService to return something the policy handles eg HttpStatusCode.InternalServerError, in order to trigger the Polly retry policy. As I stated in this answer you can't unit test such code, since the retry policy is attached to the HttpClient via the DI. Adding Polly retry policy to a mocked HttpClient? It should be easy to expand this sample to test more sophisticated policies, for example to test .SetWaitAndRetryPolicy1(). To do this, it can be helpful to mock your Polly policy to return particular results or throw particular outcomes on execution. Repeat for any more headers. Boost.Test requires that you manually create a test project. Connect and share knowledge within a single location that is structured and easy to search. We use it so often to make web requests. C# Quicktip: In Xunit how to skip a unit test from being run As suggested in the comments I recommend Simmy. If it fails with a different exception or status code, it propagates the exception to the caller. Polly is an awesome open source project part of the .Net Foundation. A test adapter integrates unit tests with the Test Explorer window. http://www.introtorx.com/Content/v1.0.10621.0/16_TestingRx.html#TestScheduler for more information. It will retry up to 3 times. This property was added in .NET 5 (finally!). During the mock setup, it stores the Dequeue value as a return instead of invoking it every time. GitHub blocks most GitHub Wikis from search engines. I actually just found what I was looking for in Polly itself! When theres an error, it retries, and then succeeds 3. This will be a different type of exception and it will also need a different solution to solve the problem. If somebody changes the configuration, the test provides regression value by failing. In the Add Reference dialog, choose the project(s) you want to test. EDIT: Improved the Unit-testing wiki to highlight this. privacy statement. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The text was updated successfully, but these errors were encountered: Hi @jiimaho A good strategy for this could be Dependency Injection: Hi @reisenberger and thanks for your quick reply. If the test code doesn't export the functions that you want to test, add the output .obj or .lib files to the dependencies of the test project. You can add traits to test methods to specify test owners, priority, and other information. Writing unit-tests to verify that Polly works can be a very valuable way to explore and understand what Polly does. Here's an example from an blockchain challenge I had to do, I execute 4 calls in a row, so if the InjectionRate is 0.25 one of the 4 calls would trigger a Polly policy: You can unit test this by mocking out the HttpClient and setting up your own test version of the WaitAndRetryAsync policy. Well occasionally send you account related emails. The .cpp file in your test project has a stub class and method defined for you. in order to trigger Polly's fault and resilience policies such as WaitAndRetry. To learn more, see our tips on writing great answers. If that code expectation is not all wired up properly inside the app, it could be a cause of test failure. Right-click on the failing test for a pop-up menu. There are many possible HTTP transient errors. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. There are many overloads that you can choose to implement. The RetryAsync () helper method will execute the API call a fixed number of times if it fails with a TooManyRequests status code. Before we jump to an actual problem of writing a test for IHttpClientFactory and HttpClient which instance is create by IHttpClientFactory, let's see how the actual setup looks like in Startup.cs class file. Since it is an interface it is easy to mock it for the class constructors, but when it comes to actual unit tests we need to mock HttpClient class instance. That's exactly the way we handle it within Polly's own specs, to allow tests to run instantly where time-delays are involved: specs either substitute SystemClock.UtcNow or SystemClock.Sleep , depending on whether the policy-under-test is waiting passively for time to pass elsewhere (as in CircuitBreaker moving to half-open) or actively controlling the delay (as in WaitAndRetry). Not the answer you're looking for? The test uses WebApplicationFactory to exercise your normal app startup in configuring the HttpClient/policy to be tested; but then pull the "test" HttpClient configuration out for a tighter unit test. This means when the retry conditions are met, it retries the request. It must be manually configured. After all the tests run, the window shows the tests that passed and the ones that failed. On the Test menu, choose Windows > Test Explorer. It will retry for a number of time when receiving any exception. You may be tempted to create additional infastructure and unit test an injected HttpClient with mocked out http responses but its simpler to just unit test the extension method. In the DI container set the handler to be applied to the injected http client, this will be avalible to the constructor of FooService. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? How can I unit test polly retry? By clicking Sign up for GitHub, you agree to our terms of service and For Boost.Test, see Boost Test library: The unit test framework. rev2023.5.1.43404. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Thank you for asking and answering the question. 0 comments Enigma94 commented on Apr 28, 2020 What I am trying to do: Throw SqlException in ExecuteAsync 2 times 3rd time return true What actually happens: Throws SqlException in ExecuteAsync 1 time Unit test fails var retryPolicy = Policy.Handle().Retry(retryCount: 3); retryPolicy.Execute(() => { mockProcessor.Object.Process(); }); //assert mockProcessor.Verify(t => t.Process(), Times.Exactly(4)); }, Note here is the simple interface used in this example public interface IProcessor { void Process(); }, //Execute the error prone code with the policy, .WaitAndRetry(retryCount: MAX_RETRIES, sleepDurationProvider: (attemptCount) => TimeSpan.FromSeconds(attemptCount *, onRetry: (exception, sleepDuration, attemptNumber, context) =>, (attemptCount) => TimeSpan.FromSeconds(attemptCount *, //Change something to try to fix the problem, IRetryDelayCalculator retryDelayCalculator, retryPolicy = Policy.Handle(ex => ex.StatusCode == HttpStatusCode.TooManyRequests). So, how does it test the integration between the HttpClient and the retry policy? SystemClock.Sleep allows me to mock the internal timer for Polly, which causes the sleeps to really not sleep. Imagine this: I want a retry on the authentication api but only when I receive a RequestTimeout (Http status code 408). I do like writing unit tests but especially when programming difficult scenarios with APIs and policies. You can download the Google Test adapter and Boost.Test Adapter extensions on the Visual Studio Marketplace. Choose the icon for more information, or to run or debug the unit test: More info about Internet Explorer and Microsoft Edge, To link the tests to the object or library files, Microsoft.VisualStudio.TestTools.CppUnitTestFramework API reference, Boost Test library: The unit test framework. Asking for help, clarification, or responding to other answers. In the DI container set the handler to be applied to the injected http client, this will be avalible to the constructor of FooService. You can do retries with and without delays. For this kind of scenarios there is a very cool library: Polly which I have been using for some years now (together with Refit) and I am just deeply in love with both libraries. Not the answer you're looking for? Testing Your Code When Using Polly | no dogma blog I am getting answers right away here. The simplest way to check how many times code was executed is by using a mock. In this testing approach, you typically stub or mock out the underlying systems called (for instance you might stub out a call to some endpoint to return TimeoutException), then check your configured policy does handle that. It allows you to inject exceptions, return BadRequests and etc. I'm trying to write a unit test for polly, but it looks like the return is cached. From the Polly repository: Polly is a .NET resilience and transient-fault-handling library that allows developers to express policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, and Fallback in a fluent and thread-safe manner. Please view the original page on GitHub.com and not this indexable For insight into how to do this, pull down the codebase and check out how Polly's own unit tests manipulate the clock. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Hi, There is a nice way to test these type of scenario using Http interceptions - using JustEat nuget, checkthis out ->. Visual Studio 2017 and later (Professional and Enterprise editions). I guess I should be able to create an exact test but for demonstration purposes this will serve its purpose. When developing an application with Polly you will also probably want to write some unit tests. Can my creature spell be countered if I cast a split second spell after it? The test simply proves that HttpClientFactory does configure the HttpClient to use the policy. To test that the retry policy is invoked, you could make the test setup configure a fake/mock ILog implementation, and (for example) assert that the expected call .Error("Delaying for {delay}ms, ") in your onRetry delegate is made on the fake logger. Now all client instances with name "sitemap" we use in our code will already have predefined base URL and retry policy configured by Polly. A test project creates a separate app that calls the code in your executable and reports on its behavior. Lets say I created a micro service to create orders. To show the results, I executed the following code several times to produce different output: Sometimes the server will return errors on every request attempt, and itll error out after 3 retry attempts: Other times itll retry a few times and then succeed: Note: I called WeatherClient.GetWeather() in a console app to produce these results. Note: You may have noticed this is checking HttpRequestException.StatusCode. To enable access to the functions in the project under test, add a reference to the project in your test project. Theres only one instance of Random, and there could be multiple threads making requests concurrently. So, this code does not test any part of the original code. How would I test what happens after we have re-tried 3 times? Guess not! All Rights Reserved. Yes, it can! Hi @PingPongSet . Some transient errors can be fixed by delaying for a short time. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Retry setting is set via a config file in JSON (e.g. And, even better, a mechanism to do some retries before throwing an exception. Thanks for that @rog1039 . For the first case I use Moq to mock the error prone code so it returns an incorrect value. In other words, it's a full end-to-end integration test. Currently I don't see a way to unit test a retry policy if you use the time-based retry policy. Use the one that makes the most sense in your scenario. Too me, this is one of the most important (and fun) parts. Not sure why, but it looks like the responses queue is only being Dequeue once, this leads me to believe the response is being cache. as GitHub blocks most GitHub Wikis from search engines. In Test Explorer, choose Run All, or select the specific tests you want to run. Create test projects in the same solution as the code you want to test. For . This will be my full AuthenticationService: Now I can test the behavior with Moq to mock the API: Let us dive a bit deeper into policies and Polly and combine different policies (and even add two more). Why are players required to record the moves in World Championship Classical games? Have a question about this project? This example shows how you can test that the constructor initializes the class the way you expect: In the previous example, the result of the Assert::AreEqual call determines whether the test passes or fails. See these example links: 1; 2; 3; 4. With Polly it is possible to create complex and advanced scenarios for error handling with just a few lines of code. But the next problem arises: the API is going to be protected with OAuth so we have to get an access token from another endpoint and provide a bearer token to be able to retrieve products. I posted the same question on StackOverflow a few weeks ago without any answer. Imagine the order api is really broken. Queston 1: Am I missing something? Which language's style guidelines should be used when writing code that is supposed to be called from another language? Do all the tests need adjusting? Suggested strategy: stub out Polly for the purposes of those tests. Ubuntu won't accept my choice of password. A boy can regenerate, so demons eat him for years. 2023 Jacob Duijzer. With both previous methods, we can use this retry logic in C# for both, Actionand Funcdelegates. Heres a simple example of using Polly to do retries with a delay. When developing an application with Polly you will also probably want to write some unit tests. Alternatively, you could write your own very short StubDelegatingHandler. This section shows syntax for the Microsoft Unit Testing Framework for C/C++. How do I stop the Flickering on Mode 13h? One of those classes is System.Net.HttpClient class. sleepDurationProvider: retryDelayCalculator.Calculate, "https://localhost:12345/weatherforecast", Executing logic between retries with the onRetry parameter, Full example Retrying HttpClient requests with Polly, WeatherClient Retries HttpClient requests with Polly, WeatherService A service stub that intentionally returns errors, Retry delay calculation: Exponential backoff with jitter, C# Check if a string contains any substring from a list. This is a simple implementation of a retry method. However, if you intended the test to exercise more directly the "test" configuration from HttpClientFactory, you may want: so that the variable client is assigned the "test" configuration from HttpClientFactory. you directly to GitHub. In .NET Core we got IHttpClientFactory which allows us to have multiple configurations for HttpClient instances so that we do not need to repeat client setup. For more information, see How to: Use CTest in Visual Studio. In addition, Ill show the exponential backoff with jitter calculator class. Whenever youre dealing with code that can run into transient errors, its a good idea to implement retries. Which was the first Sci-Fi story to predict obnoxious "robo calls"? Use DI to provide policies to consuming classes; tests can then stub out Polly by injecting NoOpPolicy in place of real policies. By clicking Sign up for GitHub, you agree to our terms of service and Sign up for a free GitHub account to open an issue and contact its maintainers and the community. :). To produce a test result, use the static methods in the Assert class to test actual results against expected results. The Circuit Breaker pattern prevents an application from performing an operation that's likely to fail. But, to allow you to concentrate on delivering your business value rather than reinventing Polly's test wheel, keep in mind that the Polly codebase tests its own operation extensively. The WeatherClient contains this single HttpClient instance. Since this application is ASP.NET Core application I will inject the service directly to controller using constructor. This class is passed into the client so it can be used as the sleepDurationProvider Polly parameter. This is useful if you have many concurrent requests because it spreads out retry attempts. Please note the new name RetryPolicyTests2 . Since there is a time element (during which the circuit breaker breaks), the number of retries can vary. A simple retry will not be enough because what if the order api is offline for a longer time? Become a Patreon and get source code access: https://www.patreon.com/nickchapsasCheck out my courses: https://nickchapsas.comThe giveaway is now over. (As at Polly v6.0, the Polly codebase has around 1700 tests per target framework.). Can I use my Coinbase address to receive bitcoin? Using the Executor Class Once we have defined the Executorclass and its methods, it is time to execute the FirstSimulationMethodand the SecondSimulationMethodmethods. Already on GitHub? Edit and build your test project or solution. Why did US v. Assange skip the court of appeal? Published with Wowchemy the free, open source website builder that empowers creators. From version 6.0.1, Polly targets .NET Standard 1.1 and 2.0+. This means every outbound call that the named-client "test" makes would return HttpStatusCode.InternalServerError; it's a minimal example of what HttpClientInterception does, but HttpClientInterception does more, does it with much more configurability, and with a nice fluent syntax. [TestMethod()] public void TestProcessor_WhenError_Retries() { //arrange var mockProcessor = new Mock(); mockProcessor.SetupSequence(p => p.Process()) .Throws() //1st attempt .Throws() //retry 1 .Throws() //retry 2 .Pass(); //retry 3 succeeds (note: it's a void method, hence Pass() instead of Returns()). The Polly policy is configured within the test. means the variable HttpClient client which the test posts on (await client.PostAsync(url, content);) is assigned the HttpClient returned from WebApplicationFactory, the HttpClient instance designed to invoke your webapp, not the "test" configuration from HttpClientFactory. Lets say you want to check if your code was retried 3 times and then successfully completed on the final attempt. Why is it shorter than a normal address? .NET Core has done a great job by introducing interface for most of classes which makes them easy to write unit tests around them. to your account. Add a jitter strategy to the retry policy If you check the constructor of HttpClient you will see that it inherits and abstract class IHttpMessageHandler which can be mocked since it is an abstract class. This can be done with a simple DummyMethod that keeps track of its invocations and has a sorted and predefined collection of response http status codes. Define and run unit tests inside one or more test projects. The following illustration shows a test project whose tests have not yet run. Hi @jiimaho Yes, that's absolutely right. Its practically a guarantee that youll eventually run into some kind of transient error. When all retry attempts fail, it fails. Can it still be improved? For example, lets say youre implementing an algorithm to calculate predictions and its prone to transient errors. Was Aristarchus the first to propose heliocentrism? Unit Testing retry policy with SqlExceptions #768 - Github In your tests, inject NoOpPolicy rather than the policies you use in production, and Polly is stubbed out of those tests. Thanks for contributing an answer to Stack Overflow! If you want to use the InjectionRate less than 1 you can use xunit and moq chaining via SetupSequence and Moq.Language.ISetupSequentialResult. Polly policies all fulfil execution interfaces (ISyncPolicy, ISyncPolicy, IAsyncPolicy and IAsyncPolicy). On retry attempts, you want to change the parameters to reduce the chances of transient errors during the next retry attempt: Note: The Fallback policy might have been a good option here, but the purpose of this is to show how to do retries without delaying. Mocking HttpClient in unit tests with Moq and Xunit when using I Honestly love this approach, thanks for the article, this was really helpful, i was able to get a simple retry working using this. Post an issue on the issues board. When you retry without a delay, it means youll be changing something that should fix the problem so that the retries succeed. It will open the circuit for a certain amount of time which means it will not even try to execute the call but immediately throw an exception. I have another question on setting system clock. Let's check it: Executor.Execute(FirstSimulationMethod, 3); Perhaps you have code modules for which you already had unit tests, including success and failure cases. The only difference is I made it randomly return the 429 error status code. tar command with and without --absolute-names option. Also, tell me if you happen to know alternative libraries, I would very much like that! What my code should do if there was no policy in place. Already on GitHub? It is documented here: Microsoft.VisualStudio.TestTools.CppUnitTestFramework API reference. Then you would know the retry had been invoked. I offer this variant in case you just want the shortest possible test of the functionality declared in a method like .SetWaitAndRetryPolicy1(). In your production code, inject the real policy you want to use. TL:DR; Polly's NoOpPolicy allows you to stub out Polly, to test your code as if Polly were not in the mix. One of these classes come from namespace System.IO for file and folder operations, but luckily there are libraries that help you write testable code using System.IO classes. You signed in with another tab or window. The unit test itself does not look so sophisticated as it would be as if you would wrap HttpClient class to implementation of an interface, but this way you get to keep using IHttpClientFactorywhich is more beneficial for your application than adapting it to much to have simpler unit tests. The "Retry pattern" enables an application to retry an operation in the expectation that the operation will eventually succeed. In this article, Ill go into more details about how to use Polly to do retries. In this simple example, I will demonstrate how to . I want to unit test a polly retry logic. Lets try and implement the same scenario in a more clean and maintainable way by using Polly! Polly allows http retries with exponential backoff so if the resource you are trying to reach throws a transient error (an error that should resolve itself) like 500 (Server Error) or 408 (Request Timeout) then the request will auto-magically be re-tried x times with an increased back-off (the period between re-tries) before giving up.
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