Using WireMock.NET in Functional testing in ASP.NET WEB API

Using WireMock.NET in Functional testing in ASP.NET WEB API


12 Articles


In this article, let's learn about how to use WireMock.NET in Functional Test in WebAPI in ASP.NET Core.

Note: If you have not done so already, I recommend you read the article on Faking Dependencies in Functional testing in ASP.NET WEB API.

Table of Contents

  1. Introduction
  2. Why to use WireMock.NET?
  3. Implementing WireMock.NET
  4. Summary


In our previous article we saw how to replace services in functional test and that approach has a drawback of writing lot of code to test all the possible scenarios. We can overcome this drawback by using WireMock.NET. It helps us to simplify the test code and also helps us to test all the possible scenarios. In this article, we'll learn about how to use WireMock.NET in functional test.

Let's start by adding Task<WeatherForecast> GetWeatherForecast() to our IExternalAPIService and implement it in ExternalAPIService. Before we dive into this implementation, lets first add URL and HttpClient configuration in our Program.cs.

Code Sample - App Settings for External API Call in Web API

Now in the Program.cs, lets add the HttpClient configuration as shown below.

Code Sample - HTTP Client Configuration

Now all we need to do is to inject the above WeatherClient HTTP Client inside our ExternalAPIService and make a call to get weather information as shown below.

Code Sample - External API call to get weather information

Next we need to call the GetWeatherForecast method from our WeatherForecastController as shown below.

Endpoint to return values from Database From API Endpoint

Here is the swagger response from the GetWeatherForecastFromAPI endpoint.

Swagger output from Endpoint to return values from API Swagger Response

Why to use WireMock.NET ?

WireMock.NET is a powerful tool that can accurately emulate the behavior of an HTTP API by capturing incoming requests and directing them to a WireMock.NET HTTP server. This capability grants us the ability to define expectations, call the API, and verify its behavior, making it ideal for extensive testing of code interactions with external services.

With WireMock.NET, we can effectively mock real API endpoints and utilize its comprehensive features for HTTP response stubbing, including matching stubs based on URL/Path, headers, cookies, and body content patterns.

The benefits of using WireMock.NET in functional tests include:

  • No need to write lot of mock code for HTTP calls. WireMock.NET helps to test actual behavior.
  • WireMock.NET helps when External API calls have rate limitation.
  • Easy to setup and cover all possible status code behaviors.

Implementing WireMock.NET

The steps to implement WireMock.NET in functional test are as follows:

  1. Add reference to WireMock.NET Nuget Package in FunctionalTest.csproj.

  2. Now Create appsettings.Test.json in FunctionalTest project and right click on the file and select Properties and set Copy to Output Directory.

  3. Now configure the appsettings.Test.json in WebHostBuilder inside CustomWebApplicationFactory in FunctionalTest.cs as shown below.

    Code Sample - appsettings.Test.json configuration in Functional Test

  4. The above configuration will replace the Weather API URL in the test. Now we need to setup the WireMock.NET server. For that we need to create Fixture to be used in all the tests. So lets create a ExternalAPIFixture class as shown below

    Code Sample - WireMock ExternalAPI Fixture to respond to API Calls

    The above class is responsible for starting the WireMock.NET server in port 50000 in https mode and also for stopping it. The key thing is the SetupGetWeather where we setup request matching particular Path in WireMock.NET server and also the response to be returned. With thi setup when we call External API in Functional Test WireMock kicks in and when the path matches, it will give the expected response to be asserted in test.

    You can refer to the WireMock.NET documentation for more details on how to setup the request and response for various cases like timeouts, auth failure, etc.

  5. Now we are left with our test. So lets add the test as shown below.

    Code Sample - Get From API Functional Test using WireMock.NET

    In the above code if you notice, we are injecting ExternalAPIFixture and using it to setup the WireMock.NET before running the test and also to stop the WireMock.NET server after the test. The SetupGetWeather method is responsible for setting up the WireMock.NET server to respond to the request.

Thats it. We are done with setup. Now the tests will run in the following flow.

  1. Start Test Method.
  2. Create HTTP Client.
  3. Create WebApplicationFactory.
  4. Run Program.cs.
  5. Service Registration.
  6. Overriding Service Registration and Configuration with ConfigureTestServices.
  7. Build Web Application.
  8. WireMock.NET Setup.
  9. Test Code Execution.

Now lets run the test and see the result.

Passing Test


In this article, we learnt about how to use WireMock.NET in functional test in ASP.NET Web API. We also saw the benefits of using WireMock.NET in functional test. The complete source code for this article can be found here. Hope you find this information useful. In our next article we will continue to learn how to setup Authentication in Functional Test in ASP.NET Web API.

  • Webapi
  • WireMock.Net
  • Functional Test
  • Integration Test