Davidortinau Maui Skills Maui Unit Testing

.NET MAUI Unit Testing — Gotchas & Best Practices

For project templates, xUnit examples, ViewModel test patterns, and CLI commands, see references/unit-testing-api.md.

⚠️ TFM Trap: Don't Use Platform-Specific TFMs

<!-- ❌ xUnit can't run on platform-specific TFMs -->
<TargetFramework>net9.0-ios</TargetFramework>

<!-- ✅ Use plain .NET TFM for desktop test host -->
<TargetFrameworks>net9.0;net10.0</TargetFrameworks>

⚠️ OutputType Trap: App Project as Test Dependency

If your test project references the app project, the app tries to build as Exe for the test TFM — this fails. Add a conditional OutputType:

<!-- ❌ App .csproj without conditional — breaks test builds -->
<OutputType>Exe</OutputType>

<!-- ✅ Library for test TFM, Exe for platform TFMs -->
<PropertyGroup Condition="'$(TargetFramework)' == 'net9.0'">
  <OutputType>Library</OutputType>
</PropertyGroup>
<PropertyGroup Condition="'$(TargetFramework)' != 'net9.0'">
  <OutputType>Exe</OutputType>
</PropertyGroup>

Common Mistakes

❌ Using Static MAUI APIs in ViewModels

ViewModels that directly call static MAUI APIs are untestable:

// ❌ Untestable — Shell.Current requires a running MAUI app
public async Task GoToDetail(int id)
    => await Shell.Current.GoToAsync($"detail?id={id}");

// ✅ Inject an interface — fully testable
public class MyViewModel(INavigationService nav)
{
    public async Task GoToDetail(int id)
        => await nav.GoToAsync($"detail?id={id}");
}

Static APIs to wrap behind interfaces:

• Shell.Current → INavigationService
• Application.Current → avoid entirely
• SecureStorage.Default → ISecureStorage
• Connectivity.Current → IConnectivity

❌ Asserting on UI Bindings Instead of ViewModel State

// ❌ Testing the binding — fragile, needs a running UI
Assert.Equal("Hello", label.Text);

// ✅ Testing the ViewModel — fast, no platform dependency
Assert.Equal("Hello", viewModel.Title);
Assert.True(viewModel.SaveCommand.CanExecute(null));

Mocking Strategy for MAUI Services

Architecture: Interface-First for Testability

Define service interfaces so ViewModels have zero MAUI platform dependencies:

// ✅ These make your entire ViewModel layer testable
public interface INavigationService
{
    Task GoToAsync(string route);
    Task GoBackAsync();
}

public interface IDialogService
{
    Task<bool> ConfirmAsync(string title, string message);
}

Register implementations in MauiProgram.cs; inject interfaces into ViewModels.

Tips

• No Application.Current or Shell.Current in ViewModels — wrap in injectable services
• Use ObservableCollection<T> and [ObservableProperty] (MVVM Toolkit) for testable state
• Assert on ViewModel properties and CanExecute, not UI bindings
• Use TaskCompletionSource to test async waiting flows
• Run dotnet test in CI to catch regressions early
• On-device tests: Use xunit.runner.devices for real platform APIs (sensors, camera, Bluetooth)

Checklist

• Test project targets plain net9.0/net10.0 (not platform-specific TFMs)
• App project has conditional OutputType for test TFM
• All MAUI static APIs wrapped behind injectable interfaces
• ViewModels tested via properties and commands, not UI bindings
• IDispatcher mocked to invoke synchronously in tests
• dotnet test runs green in CI

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