Simply set the InjectionRate to 1 to guarantee a fault in your unit test. Don't include object files that have a main function or another standard entry point such as wmain, WinMain, or DllMain. This will add quite a few extra scenarios where things can go wrong, the most commonly be timeouts and expiration of tokens. 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. This section shows syntax for the Microsoft Unit Testing Framework for C/C++. 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. Visual Studio 2017 and later (Professional and Enterprise editions). Define and run unit tests inside one or more test projects. 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. Adding Polly retry policy to a mocked HttpClient? Visual Studio 2017 and later (Professional and Enterprise editions) CodeLens lets you quickly see the status of a unit test without leaving the code editor. An understandable desire when introducing Polly to a project is to want to check the Polly policy does what it says on the tin. The Assert class contains many other methods to compare expected results with actual results. Right-click on the solution node in Solution Explorer and choose Add > New Project on the shortcut menu to add the project template. GitHub blocks most GitHub Wikis from search engines. What my code should do if there was no policy in place. In your production code, inject the real policy you want to use. For more information, see How to: Use Google Test in Visual Studio. Generic Doubly-Linked-Lists C implementation. 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. How a simple API call can get way too complex How does having the Polly policy in play affect your existing unit tests? When sending concurrent requests with HttpClient, its a good idea to use the same instance repeatedly. PolicyResult and PolicyResult have public factory methods, allowing you to mock .ExecuteAndCapture() overloads to return the PolicyResult of your choice. 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. Using the Executor Class Once we have defined the Executorclass and its methods, it is time to execute the FirstSimulationMethodand the SecondSimulationMethodmethods. 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. 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. Maybe the API is spinning up, rebooting or there might be a network issue: But what if the API throws an exception because my access token is expired? 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. Although there are abundant resources about Polly on the web I wanted to write a post with a lot of sample code to provide a quick and practical example of how easy it is to use Polly to create advanced exception handling with APIs. For more information about using Test Explorer, see Run unit tests with Test Explorer. The "Retry pattern" enables an application to retry an operation in the expectation that the operation will eventually succeed. Please view the original page on GitHub.com and not this indexable For failed tests, the message displays details that help to diagnose the cause. That is, it only sends request one time, not three times. Because WebApplicationFactory.CreateClient() has no overloads that returns the named HttpClient: Update After Comment from @reisenberger 4 Jan 2019. The app-under-test in their sample app is also using typed-clients from IHttpClientFactory; and is also using WebApplicationFactory to orchestrate the tests; so is a close fit for the test approach you have already started on. The Circuit Breaker pattern prevents an application from performing an operation that's likely to fail. How to Implement Retry Logic in C# - Code Maze Here are the scenarios I test for - How my code behaves when the policy throws an exception, such as TimeoutRejectionException, BulkheadRejectedException or BrokenCircuitException. We can include 404 (Not Found) but that depends on the use case, in some APIs 404 means the data you were looking for is not avalible. Last Modified: Mon, 23 Sep 2019 21:54:42 GMT, This page is a concise conceptual overview of different unit-testing approaches you may take with Polly. I offer this variant in case you just want the shortest possible test of the functionality declared in a method like .SetWaitAndRetryPolicy1(). When developing an application with Polly you will also probably want to write some unit tests. Well occasionally send you account related emails. #161: Simple Retry Policy with Polly - YouTube It will retry up to 3 times. He also rips off an arm to use as a sword, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). An application can combine these two patterns. The indexable preview below may have Become a Patreon and get source code access: https://www.patreon.com/nickchapsasCheck out my courses: https://nickchapsas.comThe giveaway is now over. Readme Issues Note Important Announcement: Architectural changes in v8 Sign up for a free GitHub account to open an issue and contact its maintainers and the community. There are multiple endpoints, all authenticated with OAuth.