For the first case I use Moq to mock the error prone code so it returns an incorrect value. 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. This retry policy means when an exception of type TransientException is caught, it will delay 1 second and then retry. This is useful if you have many concurrent requests because it spreads out retry attempts. You can then use these values to sort and group tests in Test Explorer. 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). It should be easy to expand this sample to test more sophisticated policies, for example to test .SetWaitAndRetryPolicy1(). When sending concurrent requests with HttpClient, its a good idea to use the same instance repeatedly. Question 2: Perhaps you have code modules for which you already had unit tests, including success and failure cases. How do I test what my code does without Polly 'interfering'? 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. Choose Debug to step through the function where the failure occurred. Adding Polly retry policy to a mocked HttpClient? For insight into how to do this, pull down the codebase and check out how Polly's own unit tests manipulate the clock. The indexable preview below may have using Polly; using System; using System.Diagnostics; using System.Net.Cache; using System.Net.Http; public class RetryClient { private HttpClient httpClient = new HttpClient (new WebRequestHandler () { CachePolicy = new HttpRequestCachePolicy (HttpRequestCacheLevel.NoCacheNoStore) }); public HttpResponseMessage PostAsyncWithRetry ( String url, Thoughts/questions about unit-testing? Polly is an awesome open source project part of the .Net Foundation. Google Test Adapter is included as a default component of the Desktop development with C++ workload. Does a password policy with a restriction of repeated characters increase security? 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. But how can we verify all these scenarios work? 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). Hi @jiimaho Yes, that's absolutely right. I updated my existing integration test method to below, but the retry policy is not activated. Using an Ohm Meter to test for bonding of a subpanel. With Polly, you can define a Retry policy with the number of retries, the exponential backoff configuration, and the actions to take when there's an HTTP exception, such as logging the error. 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. Asking for help, clarification, or responding to other answers. Thanks. Visual Studio includes these C++ test frameworks with no extra downloads required: You can use the installed frameworks, or write your own test adapter for whatever framework you want to use within Visual Studio. The Assert class contains many other methods to compare expected results with actual results. TL:DR; Polly's NoOpPolicy allows you to stub out Polly, to test your code as if Polly were not in the mix. How to unit test retry policy, First, theres three primary scenarios to verify: 1. Polly defines a NoOpPolicy for this scenario. It reduces pressure on the server, which decreases the chances of running into transient errors. 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. Ubuntu won't accept my choice of password. 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. Well occasionally send you account related emails. Choose Add > Reference. This will add quite a few extra scenarios where things can go wrong, the most commonly be timeouts and expiration of tokens. Create test projects in the same solution as the code you want to test. To add a new test project to an existing solution. 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. If you want to test the Polly policy configured on IHttpClientService within your app, via an end-to-end integration test of your app orchestrated by WebApplicationFactory, then you will have to fire the whole request at http://localhost:1234/api/v1/car/ (as your test code is already doing), and somehow stub out whatever downstream call http://localhost:1234/api/v1/car/ is making through HttpClientService. There is no need for any WebApplicationFactory, IHost, IHostedService or anything from ASP.NET. A common need is to test the logic of your system-under-test as if Polly were not part of the mix. Polly can also do other cool things listed below but Ill focus on simple retry. By clicking Sign up for GitHub, you agree to our terms of service and In this simple example, I will demonstrate how to . Can I use my Coinbase address to receive bitcoin? In your production code, inject the real policy you want to use. The microsoft example also sets .SetHandlerLifetime(TimeSpan.FromMinutes(5)). Test Explorer discovers test methods in other supported frameworks in a similar way. Why did DOS-based Windows require HIMEM.SYS to boot? There are many possible HTTP transient errors. in order to trigger Polly's fault and resilience policies such as WaitAndRetry. Example: Thanks for contributing an answer to Stack Overflow! 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. See the many tests within the existing codebase which do this. 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. I want to unit test a polly retry logic. Whenever youre dealing with code that can run into transient errors, its a good idea to implement retries. With Polly it is possible to create complex and advanced scenarios for error handling with just a few lines of code. When all retry attempts fail, it fails. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. Please view the original page on GitHub.com and not this indexable 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. When developing an application with Polly you will also probably want to write some unit tests. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond? 565), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. For this test the following should be true per invocation, services.AddHttpClient(), .OrResult(msg => msg.StatusCode == System.Net.HttpStatusCode.NotFound). I will answer the question at three different levels, and you can choose what suits best. In your test code, inject an equivalent policy that doesn't do any waiting, eg Retry (3) // etc Extract static SystemClock to interface This only tests that a mock is being called, not that the retry policy is working. Queston 1: Am I missing something? So, lets say hi to the circuit breaker. Let's say you use the following approach, and this code below is part of your method that does a few more things than executing the policy itself. Don't include object files that have a main function or another standard entry point such as wmain, WinMain, or DllMain.

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