Home While unit testing GetAsync, How to make an HttpResponseMessage returns an exception to be caught by the catch block?

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While unit testing GetAsync, How to make an HttpResponseMessage returns an exception to be caught by the catch block?

byMR

November 1, 2024

I’m unit testing a code similar to the one below. There is one use case where I want the GetAsync to throw an exception to be caught in the catch block.

try
{
   var response = await client.GetAsync(url, cancellationToken);
}
catch(Exception e)
{
  _logger.LogError(e)
}

I’m mocking the HttpClient

var factory = new Mock<IHttpClientFactory>();

var httpClient = new HttpClient(handler)
{
   BaseAddress = new Uri("http://localhost:7100")
}

factory.Setup(_ => _.CreateClient(It.IsAny<string>()))
      .Returns(httpClient)
      .Verifiable();

Here I’m mocking the HttpMessageHandler

var handler = new Mock<HttpMessageHandler>();
handler
    .Protected()
    .Setup<Task<HttpResponseMessage>>(
      "SendAsync",
      ItExpr.IsAny<HttpRequestMessage>(),
      ItExpr.IsAny<CancellationToken>()
    )
    .Returns(GetHttpResponseMessage())
    .Verifiable();

GetHttpResponseMessage() is the method where I put the logic to return the appropriate HttpResponseMassage.

HttpResponseMessage GetHttpResponseMessage(int code)
{
   if(code == 200)
   {
      return new HttpResponseMessage{ StatusCode = HttpStatusCode.OK };

   }
   else if(code == 500)
   {
      //StatusCode.InternalServerError   ???
      //throw new Exception() ???
   }
}

None of those 2 above is working. Neither one is causing an exception to be caught by the catch block.

Thanks for helping

>Solution :

You can setup the async method to throw an exception directly

using Moq;
using Moq.Protected;
using System;
using System.Net;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

public class YourTestClass
{
    public void TestMethod()
    {
        var factory = new Mock<IHttpClientFactory>();

        var handler = new Mock<HttpMessageHandler>();
        handler
            .Protected()
            .Setup<Task<HttpResponseMessage>>(
                "SendAsync",
                ItExpr.IsAny<HttpRequestMessage>(),
                ItExpr.IsAny<CancellationToken>()
            )
            .Throws(new HttpRequestException("Simulated exception"))
            .Verifiable();

        var httpClient = new HttpClient(handler.Object)
        {
            BaseAddress = new Uri("http://localhost:7100")
        };

        factory.Setup(_ => _.CreateClient(It.IsAny<string>()))
              .Returns(httpClient)
              .Verifiable();

        
        try
        {
           
        }
        catch (HttpRequestException ex)
        {
         
        }
    }
}