Create test projects in the same solution as the code you want to test. A common need is to test the logic of your system-under-test as if Polly were not part of the mix. At the end, Ill show a full example of retrying HttpClient requests with Polly. TEST_CLASS and TEST_METHOD are part of the Microsoft Native Test Framework. invoking the "test" configuration from HttpClientFactory (as I believe it should, from what you have described as the code intention). rendering errors, broken links, and missing images. HTTP Retry with Polly | Carl Paton | There are no silly questions Can my creature spell be countered if I cast a split second spell after it? The button and/or link above will take Next, in your unit test .cpp file, add an #include directive for any header files that declare the types and functions you want to test. Changing it to () => responses.Dequeue() works now. Let's check it: Executor.Execute(FirstSimulationMethod, 3); 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. When the configured delay time has been passed it will reset the circuit and start all over. While this is not a complete solution it can already handle some issues. As suggested in the comments I recommend Simmy. Does a password policy with a restriction of repeated characters increase security? Decorator pattern. A real example in C# Just Some Code - GitHub Pages How can I unit test polly retry? But how can we verify all these scenarios work? (It's slightly questionable whether SystemClock should really be public that inherited from before AppvNext stewardship of Polly SystemClock is really an internal concern but it does have this benefit for user testing.). 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. privacy statement. I will answer the question at three different levels, and you can choose what suits best. What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond? How my code behaves when the policy throws an exception, such as TimeoutRejectionException, BulkheadRejectedException or BrokenCircuitException. How to verify that method was NOT called in Moq? This means when the retry conditions are met, it retries the request. Too me, this is one of the most important (and fun) parts. There are no ads in this search engine enabler service. That is, it only sends request one time, not three times. @reisenberger I think it's good to let consumers of the Polly API be able to provide a time-provider. 1. If you write your own integration tests around policies in your project, note the possibility to manipulate Polly's abstracted SystemClock. 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. 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. See here Some time ago I wrote an article which explains how to Increase service resilience using Polly and retry pattern in ASP.NET Core. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Thank you for asking and answering the question. So heres an example of writing a unit test for test scenario 2. ErrorProneCode.cs is the unreliable class that I will mock and pass mocked policies into. C# - How to use Polly to do retries | MAKOLYTE In your test code, inject an equivalent policy that doesn't do any waiting, eg Retry (3) // etc Extract static SystemClock to interface If you want to know more of how to easily retry and make your application more resilient to poor and unstable network connection check articleIncrease service resilience using Polly and retry pattern in ASP.NET Core. Install nuget Microsoft.Extensions.Http.Polly. The simplest way to check how many times code was executed is by using a mock. On the Test menu, choose Windows > Test Explorer. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. I offer this variant in case you just want the shortest possible test of the functionality declared in a method like .SetWaitAndRetryPolicy1(). If there are going to be many concurrent requests, then it makes sense to use the exponential backoff with jitter strategy. 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. Alternatively, you could write your own very short StubDelegatingHandler. Please note the new name RetryPolicyTests2 . Visual Studio 2017 and later (Professional and Enterprise editions). This integration can be tested via an integration or component test. During the mock setup, it stores the Dequeue value as a return instead of invoking it every time. Theres only one instance of Random, and there could be multiple threads making requests concurrently. Some features such as Live Unit Testing, Coded UI Tests and IntelliTest aren't supported for C++. Refactor to inject the Policy into the method/class using it (whether by constructor/property/method-parameter injection - doesn't matter). Some transient errors can be fixed by delaying for a short time. Please tell me if you have started using Polly. Can it still be improved? HttpClient relies on the HttpMessageHandler.SendAsync method, so we can mock this method and class and pass it to the constructor or HttpClient class instance. How does having the Polly policy in play affect your existing unit tests? It has helped me a lot today, github.com/App-vNext/Polly/blob/master/src/Polly.SharedSpecs/, How a top-ranked engineering school reimagined CS curriculum (Ep. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? 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. The WeatherClient contains this single HttpClient instance. Choose Debug to step through the function where the failure occurred. The "Retry pattern" enables an application to retry an operation in the expectation that the operation will eventually succeed. I want to find out how Polly retry polly configured via Startup.ConfigureServices() can be tested. This spreads out retry attempts so that youre not sending all of the retry attempts at once. Writing unit-tests to verify that Polly works can be a very valuable way to explore and understand what Polly does. Boolean algebra of the lattice of subspaces of a vector space? Newbie unit testing - Help needed : r/dotnet - Reddit If you havent already, install the Polly nuget package by executing this command (this is using View > Other Windows > Package Manager Console): After that, to use Polly, add the following using statement: The onRetry parameter allows you to pass in a lambda that will be executed between retries. Let us know how you get on with that - or if you can envisage ways it could be improved (I can envisage some - as ever, with trade-offs). A test project creates a separate app that calls the code in your executable and reports on its behavior. There are many overloads that you can choose to implement. For failed tests, the message displays details that help to diagnose the cause. What are the advantages of running a power tool on 240 V vs 120 V? Should_Return_999_When_TimeoutRejectedException_Thrown, // if there is a TimeoutRejectedException in this CallSomeSlowBadCode it will return 999, Using the HttpClientInterception to Test Methods That Use a HttpClient, Polly with .NET 6, Part 8 - Policy Registry with Minimal APIs, and HttpClientFactory, Polly with .NET 6, Part 7 - Policy Wraps with Minimal APIs, and HttpClientFactory, Polly with .NET 6, Part 6 - Policy Wraps with Minimal APIs, Polly with .NET 6, Part 5 - Using a Cancellation Token.