How to Mock Kiota API Clients

Problem

You want to develop and test your Uno app using mock API data, without changing your generated Kiota API client or API code.

Solution

The Chefs app uses the USE_MOCKS compile-time constant to control API mocking. When enabled, a custom MockHttpMessageHandler is registered as a DelegatingHandler in the HttpClient pipeline. This allows you to mock server responses at the HTTP level.

  1. Enable Mocking

    Add a USE_MOCKS constant to your build constants and set it to true.

    <PropertyGroup Condition="'$(UseMocks)'=='true'">
    <DefineConstants>$(DefineConstants);USE_MOCKS</DefineConstants>
</PropertyGroup>

  2. Configure Kiota Client to Use the Mock Handler

    In App.xaml.host.cs, when USE_MOCKS is defined, configure the Kiota client to use your mock handler:

    services.AddTransient<MockHttpMessageHandler>();
services.AddKiotaClient<ChefsApiClient>(
    context,
    options: new EndpointOptions { Url = "http://localhost:5116" }
#if USE_MOCKS
    , configure: (builder, endpoint) => builder.ConfigurePrimaryAndInnerHttpMessageHandler<MockHttpMessageHandler>()
#endif
);

  3. Implement Your Mock Handler

    Your custom MockHttpMessageHandler inspects requests and returns mock responses based on local data, without ever hitting the real API server.

    public class MockHttpMessageHandler : HttpMessageHandler
{
    // ...endpoint setup omitted for brevity...

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
    var mockResponse = new HttpResponseMessage(HttpStatusCode.OK)
    {
        Content = new StringContent(await GetMockData(request), Encoding.UTF8, "application/json")
    };

    return await Task.FromResult(mockResponse);
    }

    private async Task<string> GetMockData(HttpRequestMessage request)
    {

        // Handle Notifications
        if (request.RequestUri.AbsolutePath.Contains("/api/Notification"))
        {
            return await _mockNotificationEndpoints.HandleNotificationsRequest(request);
        }
        ...

        return "{}";
    }
}

  4. Use the Kiota Client

    Consumers of the ChefsApiClient remain unchanged:

    public class NotificationService(ChefsApiClient client) : INotificationService
    {
        public async ValueTask<IImmutableList<Notification>> GetAll(CancellationToken ct)
        {
            var notificationsData = await client.Api.Notification.GetAsync(cancellationToken: ct);
            return notificationsData?.Select(n => new Notification(n)).ToImmutableList() ?? ImmutableList<Notification>.Empty;
        }
    }

Why This Pattern?

  • No changes to Kiota-generated code.

  • Mocking is controlled by a build constant, making it easy to switch between real and mock APIs.

  • The rest of the app interacts with the API exactly as it would in production.

Source Code

Documentation