HttpClientFactoryExtensionGenerator.md

HTTP Client Factory Extension Generator

When your test project references Microsoft.Extensions.Http, this generator creates a WithHttpClientFactory() extension method for AutoMocker that provides a testable IHttpClientFactory implementation.

Features

• Automatically generates when Microsoft.Extensions.Http is referenced
• Provides a testable IHttpClientFactory backed by the same Mock<HttpMessageHandler> used by HttpClientResolver
• Caches one HttpClient per client name: calling CreateClient with the same name returns the same instance, different names return distinct instances
• Existing SetupHttp* and VerifyHttp* helpers apply to all named clients, since they share the same testable handler

Usage

public class CatalogService
{
    private readonly HttpClient _client;

    public CatalogService(IHttpClientFactory httpClientFactory)
    {
        _client = httpClientFactory.CreateClient("catalog");
    }

    public Task<HttpResponseMessage> GetProductAsync(string id)
        => _client.GetAsync($"/products/{id}");
}

[TestClass]
public class CatalogServiceTests
{
    [TestMethod]
    public async Task Test_WithHttpClientFactory()
    {
        // Arrange
        AutoMocker mocker = new();
        mocker.WithHttpClientFactory();
        mocker.SetupHttpGet("/products/1")
            .ReturnsHttpResponse(HttpStatusCode.OK, """{"id": "1"}""");

        // Act
        var service = mocker.CreateInstance<CatalogService>();
        var response = await service.GetProductAsync("1");

        // Assert
        Assert.AreEqual(HttpStatusCode.OK, response.StatusCode);
    }
}

Generated Extension Method

The generator creates:

public static AutoMocker WithHttpClientFactory(this AutoMocker mocker)
{
    // Registers a resolver that provides IHttpClientFactory
    // Returns mocker for fluent chaining
}

How It Works

The WithHttpClientFactory() method:

1. Inserts a resolver after the CacheResolver in the resolver chain
2. When IHttpClientFactory is requested, the resolver returns a testable factory implementation
3. Calling CreateClient(name) on that factory looks up (or creates) an HttpClient for the given name in an internal ConcurrentDictionary<string, HttpClient>, keyed with ordinal string comparison
4. Every cached HttpClient wraps the same Mock<HttpMessageHandler> used by HttpClientResolver, so requests made through any named client are visible to the existing SetupHttp*/VerifyHttp* helpers

This ensures any class depending on IHttpClientFactory receives a working implementation, without requiring a full dependency injection container, and without needing separate setup per client name.

Advanced Usage

Same Name Returns the Same Client

[TestMethod]
public void Test_SameNameReturnsSameClient()
{
    AutoMocker mocker = new();
    mocker.WithHttpClientFactory();
    var factory = mocker.Get<IHttpClientFactory>();

    var first = factory.CreateClient("catalog");
    var second = factory.CreateClient("catalog");

    Assert.AreSame(first, second);
}

Different Names Return Different Clients

[TestMethod]
public void Test_DifferentNamesReturnDifferentClients()
{
    AutoMocker mocker = new();
    mocker.WithHttpClientFactory();
    var factory = mocker.Get<IHttpClientFactory>();

    var catalog = factory.CreateClient("catalog");
    var orders = factory.CreateClient("orders");

    Assert.AreNotSame(catalog, orders);
}

Combining with Other Extensions

[TestMethod]
public void Test_CombinedExtensions()
{
    AutoMocker mocker = new();
    mocker.WithHttpClientFactory()
          .WithFakeLogging();

    var service = mocker.CreateInstance<CatalogService>();
    // Verify both HTTP and logging behavior
}

Disabling the Generator

You can disable this generator using an MSBuild property in your test project's .csproj file:

<PropertyGroup>
  <EnableMoqAutoMockerHttpClientFactoryGenerator>false</EnableMoqAutoMockerHttpClientFactoryGenerator>
</PropertyGroup>

Example: Disabling in Project File

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net10.0</TargetFramework>

    <!-- Disable HTTP Client Factory Extension Generator -->
    <EnableMoqAutoMockerHttpClientFactoryGenerator>false</EnableMoqAutoMockerHttpClientFactoryGenerator>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Moq.AutoMock" Version="4.0.1" />
  </ItemGroup>
</Project>

Troubleshooting

Extension Method Not Available

1. Verify your project references Microsoft.Extensions.Http
2. Check that the generator is not disabled in your .csproj
3. Rebuild the project to trigger generator execution
4. Ensure you're using the Moq.AutoMock namespace

IHttpClientFactory Not Resolving

1. Make sure you call WithHttpClientFactory() before calling CreateInstance<T>()
2. Verify the service under test accepts IHttpClientFactory (not a concrete HttpClient)

Best Practices

• Call WithHttpClientFactory() early in your test setup, before creating instances
• Use SetupHttpGet/SetupHttpPost/etc. as usual — they apply to all named clients since they share the same testable handler
• Combine with HttpClientResolver's direct HttpClient support when a class depends on both a concrete HttpClient and IHttpClientFactory

See Also

• AutoMocker API Reference
• Source Generators Overview
• HttpClient Support
• Moq.AutoMock on NuGet