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. 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. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. I want to add a delay when I receive a timeout. For the first case I use Moq to mock the error prone code so it returns an incorrect value. Why is it shorter than a normal address? It will retry up to 3 times. In Test Explorer, choose Run All, or select the specific tests you want to run. c# - Polly retry unit test - Stack Overflow It is possible simply to new up a ServiceCollection; configure a named client using HttpClientFactory; get the named client back from the IServiceProvider; and test if that client uses the policy. Polly is able to wrap different policies to handle different scenarios: While this is not the way I would structure my code in a real app, I believe this is understandable and maintainable code. For more information, see How to: Use Boost.Test in Visual Studio. That could be with a full DI container, or just simple constructor injection or property injection, per preference. Also, the shown code might not always show the best way to implementat things, it is just an example to explain some use cases of Polly. It reduces pressure on the server, which decreases the chances of running into transient errors. 2023 Jacob Duijzer. See these example links: 1; 2; 3; 4. The button and/or link above will take We do not want to loose any order because this will directly result in money loss. @reisenberger I think it's good to let consumers of the Polly API be able to provide a time-provider. This class is passed into the client so it can be used as the sleepDurationProvider Polly parameter. Disclaimer: this article and sample code have nothing to do with the work I did for the eCommerce website. Setting upIHttpClientFactory is quite easy in ASP.NET Core container setup in Startup.cs. in order to trigger Polly's fault and resilience policies such as WaitAndRetry. In the DI container set the handler to be applied to the injected http client, this will be avalible to the constructor of FooService. The signatures use the TEST_CLASS and TEST_METHOD macros, which make the methods discoverable from the Test Explorer window. This brings us to unit testing. Was Aristarchus the first to propose heliocentrism? When you use code like this in a production environment you will quickly find out that there is a need of exception handling. 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. 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. Please note the new name RetryPolicyTests2 . Have a question about this project? For Google Test documentation, see Google Test primer. Theres only one instance of Random, and there could be multiple threads making requests concurrently. For more information about using Test Explorer, see Run unit tests with Test Explorer. Thanks again for the prompt reply and the great answer. 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. Making statements based on opinion; back them up with references or personal experience. In this article, Ill go into more details about how to use Polly to do retries. So, this code does not test any part of the original code. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? 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. Become a Patreon and get source code access: https://www.patreon.com/nickchapsasCheck out my courses: https://nickchapsas.comThe giveaway is now over. Please refer to my updated comments at the bottom of OP. 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. How my code behaves when a policy becomes active and changes the outcome of a call, such as when an unreliable request works because Polly performs a retry. ErrorProneCode.cs is the unreliable class that I will mock and pass mocked policies into. While this is not a complete solution it can already handle some issues. Which was the first Sci-Fi story to predict obnoxious "robo calls"? I am using polly to handle retry (see below code). It has a project template that you can add to a solution. They provide schedulers that can be used control the flow of time which makes testing various scenarios relating to time passage very easy, repeatable, and makes unit tests very quick (Can simulate minute/hours/days/etc of time passage instantly). Parabolic, suborbital and ballistic trajectories all follow elliptic paths. This week I was connecting an eCommerce web application to an ERP system with REST APIs. TL;DR Mock your policies to return or throw particular outcomes, to test how your code responds. Simply set the InjectionRate to 1 to guarantee a fault in your unit test. In the DI container set the handler to be applied to the injected http client, this will be avalible to the constructor of FooService. HTTP Retry with Polly | Carl Paton | There are no silly questions 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. 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. Want to learn more about Polly? I want an advanced scenario that looks like this: I will not implement authentication in this flow but I guess you can already imagine: a) the flow will be much more complicated, b) it will still be quite easy to implement with Polly using the example from above. Use the one that makes the most sense in your scenario. Heres a simple example of using Polly to do retries with a delay. To produce a test result, use the static methods in the Assert class to test actual results against expected results. Also, tell me if you happen to know alternative libraries, I would very much like that! 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. - Peter Csala Jul 24, 2022 at 16:07 Updated Integration Test method Changing it to () => responses.Dequeue() works now. Not sure how to check whether the retry policy is triggered three times when ever client throws timeout Advertisement Using the Executor Class Once we have defined the Executorclass and its methods, it is time to execute the FirstSimulationMethodand the SecondSimulationMethodmethods. You may want to test how your code reacts to results or faults returned by an execution through Polly. I added the circuit breaker to the order service: All unit tests will still succeed because the circuit breaker will only break after 10 exceptions. Generating points along line with specifying the origin of point generation in QGIS, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). C# - How to use Polly to do retries | MAKOLYTE This will be a different type of exception and it will also need a different solution to solve the problem. you directly to GitHub. I have a few classes to demonstrate these scenarios, BusinessLogic.cs and OtherBusinessLogic.cs are the classes under test. By clicking Sign up for GitHub, you agree to our terms of service and It will break when the configured number of exceptions have been thrown. With Polly it is possible to create complex and advanced scenarios for error handling with just a few lines of code. :). How to verify that method was NOT called in Moq? This property was added in .NET 5 (finally!). After all the tests run, the window shows the tests that passed and the ones that failed. See the many tests within the existing codebase which do this. Mocking HttpClient in unit tests with Moq and Xunit when using There are still a lot of classes that we use daily in our code which we do not realize we cannot easily test until we get to writing unit tests for our existing code. 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. as a singleton or in the constructor of the service, this having the same scope as the service itself). In this simple example, I will demonstrate how to . Now all client instances with name "sitemap" we use in our code will already have predefined base URL and retry policy configured by Polly. C# - Retry Pattern with Polly - Code4Noobz The following sections show the basic steps to get you started with C++ unit testing. Finally, it executes the requests with HttpClient with the retry policy. #161: Simple Retry Policy with Polly - YouTube tar command with and without --absolute-names option. Test Polly retry polly configured via Startup.ConfigureServices() with ASP.NET Core API. Other errors may require you to do something to fix the problem so that the retry attempt will work. I don't want to wait more than one minute in my tests. and configure it after the Polly policy on the HttpClient ('inside' the Polly policy , it terms of the nested DelegatingHandlers). This makes it like a half-integration, half-unit test. Polly is a .NET resilience and transient-fault-handling library that allows developers to express policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, Rate-limiting and Fallback in a fluent and thread-safe manner. Readme Issues Note Important Announcement: Architectural changes in v8 Already on GitHub? I actually just found what I was looking for in Polly itself! Its practically a guarantee that youll eventually run into some kind of transient error. I use a seeded random number generator that produces an known sequence to return values from the ErrorProneCode class. For more information, see Install third-party unit test frameworks. For examples taking this concept further with PolicyRegistry or a policy factory, see our Unit testing with examples page. I cannot retrieve the HttpClient that has been configured with the Polly polly. 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. This is what the flow will look like in code: And the unit test to test the full flow (check the repository on Github to see the mock setups): So now we have a retry and a fallback. Do all the tests need adjusting? What's the function to find a city nearest to a given latitude? This can be simple, like hardcoding a delay time: You can use the attempt count in the calculation, like this: The most complex calculation is the exponential backoff with jitter strategy (Note: This is implemented in the HttpClient example section below). Discover .NET - Polly From version 6.0.1, Polly targets .NET Standard 1.1 and 2.0+. Instead it inherits HttpMessageInvoker class. When you retry with a delay, it means you think the the transient error will go away by itself after a short period of time. In other words, it's a full end-to-end integration test. Some time ago I wrote an article which explains how to Increase service resilience using Polly and retry pattern in ASP.NET Core. Right-click on the solution node in Solution Explorer and choose Add > New Project on the shortcut menu to add the project template. The 3rd parameter of onRetry is an int which represents retryAttempt, this can be added to logs. You can do retries with and without delays. If somebody changes the configuration, the test provides regression value by failing. Too me, this is one of the most important (and fun) parts.