maui-unit-testing

MAUI Unit Testing

Use this skill to make MAUI app logic testable without requiring every test to start a device or simulator. Keep UI framework dependencies at the edges.

Workflow

1. Identify what is being tested: ViewModel, service, navigation abstraction, storage wrapper, platform capability, or UI integration.
2. For ViewModels and services, create a normal xUnit test project.
3. Introduce interfaces around platform APIs such as geolocation, preferences, secure storage, media picker, file picker, and navigation.
4. Use fakes or mocks for those interfaces in unit tests.
5. Use device/integration tests only for behavior that requires handlers, platform permissions, native controls, or OS services.
6. If a test or tooling project must reference a MAUI app project, use the AppProjectReference support provided by Microsoft.Maui.Build.AppProjectReference instead of forcing the app project to behave like a normal class library.

Test Boundary Guide

ViewModel Test Pattern

Always show at least a happy-path test AND an error/edge-case test. Use a mocking library (NSubstitute, Moq) or a hand-rolled fake — both are valid.

public sealed class ProductsViewModelTests
{
    [Fact]
    public async Task LoadAsync_ServiceReturnsProducts_PopulatesProducts()
    {
        var service = Substitute.For<IProductsService>();
        service.LoadAsync().Returns([new Product("Coffee")]);
        var viewModel = new ProductsViewModel(service);

        await viewModel.LoadAsync();

        Assert.Single(viewModel.Products);
        Assert.Equal("Coffee", viewModel.Products[0].Name);
    }

    [Fact]
    public async Task LoadAsync_ServiceThrows_SetsErrorState()
    {
        var service = Substitute.For<IProductsService>();
        service.LoadAsync().Returns(Task.FromException<IReadOnlyList<Product>>(
            new HttpRequestException("offline")));
        var viewModel = new ProductsViewModel(service);

        await viewModel.LoadAsync();

        Assert.Empty(viewModel.Products);
        Assert.NotNull(viewModel.ErrorMessage);
    }
}