如何在 .NET 中为类型化客户端编写集成测试

Question

I have a .NET 7 console application that fetches data from an API.

The console application is simple and uses a "typed client", that I am writing:

services.AddSingleton<IMyTypedClient, MyTypedClient>();
services.AddHttpClient<IMyTypedClient, MyTypedClient>(client =>
    {
        client.BaseAddress = new Uri("http://www.randomnumberapi.com/api/v1.0/");
    })
    .SetHandlerLifetime(TimeSpan.FromMinutes(5))
    .AddPolicyHandler(GetRetryPolicy());

static IAsyncPolicy<HttpResponseMessage> GetRetryPolicy()
{
    return HttpPolicyExtensions
        .HandleTransientHttpError()
        .OrResult(msg => msg.StatusCode == System.Net.HttpStatusCode.NotFound)
        .WaitAndRetryAsync(6, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)));
}

Here is the "typed client":

public class MyTypedClient : IMyTypedClient
{
    private readonly HttpClient _httpClient;

    public MyTypedClient(HttpClient httpClient)
    {
        _httpClient = httpClient;
    }

    public void GetRandomNumber()
    {
        var response = _httpClient.GetAsync("/random?min=1&max=10&count=5").Result;
        if (response.StatusCode != HttpStatusCode.OK)
        {
            throw new Exception("Failed to get random number");
        }
    }
}

The above code is inspired by MS documentation .

Question I would like to integration test the "typed client" part of the app that I am writing while developing it, but how do I create integration tests for this typed client that takes a HttpClient ?

Answer 1

If you want to 'just' test the "typed client" you should not connect it to the external service during the test. You would have to provide a mock for the HttpClient in this case and inject that during the tests. This mock would have to return predictable results.

If you do want to use the external service, the test becomes very brittle because you cannot predict and therefore check if the results are correct.

In both cases testing will be hard because the typed client does not return anything, this makes is impossible to check the results.

Answer 2

I ended up just doing the following helper method in my "test" fixture:

    const string baseUrl = "https://someurl";
    const string accessToken = "token";

    var httpClient = new HttpClient
    {
        BaseAddress = new Uri(baseUrl)
    };


    return new MyTypedClient(httpClient, accessToken);