preview if you intend to, Click / TAP HERE TO View Page on GitHub.com , https://github.com/App-vNext/Polly/wiki/Unit-testing-with-Polly. 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. Thoughts/questions about unit-testing? They show an example of how to write test code. Already on GitHub? Yes, it can! 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. Well occasionally send you account related emails. See these example links: 1; 2; 3; 4. In your tests, inject NoOpPolicy rather than the policies you use in production, and Polly is stubbed out of those tests. Making statements based on opinion; back them up with references or personal experience. 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. If you want to use the InjectionRate less than 1 you can use xunit and moq chaining via SetupSequence and Moq.Language.ISetupSequentialResult. Lets work on another revision of the code to add extra retries for these scenarios: I am going to stop right here. @reisenberger I agree with @jiimaho in that there should be a supported way to manipulate the passage of time. Initialize CodeLens for a C++ unit test project in any of the following ways: Edit and build your test project or . A TEST_METHOD returns void. Running this outputs the following: 03:22:26.56244 Attempt 1 03:22:27.58430 Attempt 2 03:22:28.58729 Attempt 3 03:22:29.59790 Attempt 4 Unhandled exception. 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. If it fails with a different exception or status code, it propagates the exception to the caller. The .cpp file in your test project has a stub class and method defined for you. In this simple example, I will demonstrate how to . Boolean algebra of the lattice of subspaces of a vector space? The Circuit Breaker pattern prevents an application from performing an operation that's likely to fail. To learn more, see our tips on writing great answers. To do this, it can be helpful to mock your Polly policy to return particular results or throw particular outcomes on execution. appsettings.json). Create test projects in the same solution as the code you want to test. In this example, Im using the following service stub that randomly returns the Too Many Requests (status code 429) error response: Note: This is the WeatherForecastController class that Visual Studio auto-generates for you when you use the ASP.NET Web API template. Not the answer you're looking for? Define and run tests inside one or more test projects. This only tests that a mock is being called, not that the retry policy is working. 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. Then you would know the retry had been invoked. http://www.introtorx.com/Content/v1.0.10621.0/16_TestingRx.html#TestScheduler for more information. In your production code, inject the real policy you want to use. For more information, see Install third-party unit test frameworks. 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. It should be easy to expand this sample to test more sophisticated policies, for example to test .SetWaitAndRetryPolicy1(). Ubuntu won't accept my choice of password. When you add new source files to your project, update the test project dependencies to include the corresponding object files. Has the Melford Hall manuscript poem "Whoso terms love a fire" been attributed to any poetDonne, Roe, or other? Can I use an 11 watt LED bulb in a lamp rated for 8.6 watts maximum? So, how does it test the integration between the HttpClient and the retry policy? By clicking Sign up for GitHub, you agree to our terms of service and URL: https://github.com/App-vNext/Polly/wiki/Unit-testing-with-Polly. For failed tests, the message displays details that help to diagnose the cause. This is useful if you have many concurrent requests because it spreads out retry attempts. Imagine this: I want a retry on the authentication api but only when I receive a RequestTimeout (Http status code 408). In your test code, inject an equivalent policy that doesn't do any waiting, eg Retry (3) // etc Extract static SystemClock to interface Use DI to provide policies to consuming classes; tests can then stub out Polly by injecting NoOpPolicy in place of real policies. After the final attempt, it stopped retrying and let the exception bubble up. I want to add a delay when I receive a timeout. 1. 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. Ideally when you need to mock something that is not and abstract class or interface you could always wrap it a class that implements interface which you could mock later. 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. If you write your own integration tests around policies in your project, note the possibility to manipulate Polly's abstracted SystemClock. Well occasionally send you account related emails. privacy statement. For the first case I use Moq to mock the error prone code so it returns an incorrect value. 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. That is, it only sends request one time, not three times. Refactor to inject the Policy into the method/class using it (whether by constructor/property/method-parameter injection - doesn't matter). 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. When theres an error, it retries, and then succeeds 3. I posted the same question on StackOverflow a few weeks ago without any answer. TL;DR: Configure a mock of the underlying system to return faults the policies should handle. In the DI container set the handler to be applied to the injected http client, this will be avalible to the constructor of FooService. really helpful. In addition, it creates and contains the AsyncRetryPolicy (Note: You could pass it in instead). Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Does a password policy with a restriction of repeated characters increase security? SystemClock.Sleep allows me to mock the internal timer for Polly, which causes the sleeps to really not sleep. 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, Assert.Equal (4, Add (2, 2)); } In order to skip a test (or fact) you need to pass in the skip parameter, followed by a reason why you decided to skip the test. 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. 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. Finally, I want to verify that my code will work if no Polly policy is in use. (in response to "I cannot retrieve the HttpClient that has been configured with the Polly polly"), (to respond to the question title: "Test Polly retry polly configured via Startup.ConfigureServices() with ASP.NET Core API"). Can you still use Commanders Strike if the only attack available to forego is an attack against an ally? It reduces pressure on the server, which decreases the chances of running into transient errors. 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. TL:DR; Bear in mind the Polly codebase already tests this for you extensively. I updated my existing integration test method to below, but the retry policy is not activated. It will break when the configured number of exceptions have been thrown. There is no need for any WebApplicationFactory, IHost, IHostedService or anything from ASP.NET. Let's check it: Executor.Execute(FirstSimulationMethod, 3); Running unittest with typical test directory structure, Different return values the first and second time with Moq. Additionally, we want to be able to make our methods that rely on Polly unit testable. Polly can also do other cool things listed below but Ill focus on simple retry. I want to unit test a polly retry logic. In addition, Ill show the exponential backoff with jitter calculator class. The indexable preview below may have In this section, Ill only try to handle one: the Too Many Requests error response (429). @reisenberger I think it's good to let consumers of the Polly API be able to provide a time-provider. If this should be done through SystemClockor not i'm not sure, however in our scenario it's perfect for testability. To make sure all calls to the APIs will have a high success rate I had to implement retry mechanisms for different scenarios. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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). Define and run unit tests inside one or more test projects. Have a question about this project? I guess I should be able to create an exact test but for demonstration purposes this will serve its purpose. We use it so often to make web requests. TL:DR; Polly's NoOpPolicy allows you to stub out Polly, to test your code as if Polly were not in the mix. Why did DOS-based Windows require HIMEM.SYS to boot? You can configure these methods on a mock policy, to return or throw faults you want to simulate. Test Explorer discovers test methods in other supported frameworks in a similar way. Thanks again for the prompt reply and the great answer. Here onRetryAsync is passed a deligate inline method that just writes out a message. Do all the tests need adjusting? Please refer to my updated comments at the bottom of OP. If somebody changes the configuration, the test provides regression value by failing. What positional accuracy (ie, arc seconds) is necessary to view Saturn, Uranus, beyond? Asking for help, clarification, or responding to other answers. 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. 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. in order to trigger Polly's fault and resilience policies such as WaitAndRetry. I updated my existing integration test method to below, but the retry policy is not activated. The Assert class contains many other methods to compare expected results with actual results. The class below implements this calculation: (1 second * 2^attemptCount-1) + random jitter between 10-200ms. 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). github.com/justeat/httpclient-interception, How a top-ranked engineering school reimagined CS curriculum (Ep. Lets say I have a micro service with an API endpoint to retrieve products: Could everything just be as simple as that. Now all client instances with name "sitemap" we use in our code will already have predefined base URL and retry policy configured by Polly. Connect and share knowledge within a single location that is structured and easy to search. It was just a trigger for me to write about Polly. 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. When the configured delay time has been passed it will reset the circuit and start all over. The basic configuration is similar for both the Microsoft and Google Test frameworks. Create the projects in the same solution as the code you want to test. 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. The test can be read as a specification of the resilience behaviour for that piece of code. To enable access to the functions in the project under test, add a reference to the project in your test project. Want to learn more about Polly? The test simply proves that HttpClientFactory does configure the HttpClient to use the policy. To avoid having to type the full path in each include statement in the source file, add the required folders in Project > Properties > C/C++ > General > Additional Include Directories. :). How would I test what happens after we have re-tried 3 times? All Rights Reserved. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. Lets say you want to check if your code was retried 3 times and then successfully completed on the final attempt. Published with Wowchemy the free, open source website builder that empowers creators. Passing negative parameters to a wolframscript, Reading Graduated Cylinders for a non-transparent liquid. Sign in (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.). To do this, I pass in a NoOp policy. In the next case I verify that the application has correctly used the retry policy method. 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. Whenever youre dealing with code that can run into transient errors, its a good idea to implement retries. You should only retry if the attempt has a chance of succeeding. The following illustration shows a test project whose tests have not yet run. 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. This retry policy means when an exception of type TransientException is caught, it will delay 1 second and then retry.
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