Mocking Xamarin.Forms

FormsTests.cs

public abstract class FormsTests
{
    static FormsTests()
    {
        // Force loading of XAML assembly.
        Debug.WriteLine(typeof(XamlCompilationAttribute).FullName);

        var mock = new Mock<IPlatformServices> { DefaultValue = DefaultValue.Mock };
        mock.Setup(x => x.BeginInvokeOnMainThread(It.IsAny<Action>()))
            .Callback<Action>(action => action());

        mock.Setup(x => x.CreateTicker()).Returns(new TestTicker());
        mock.Setup(x => x.GetAssemblies()).Returns(() => AppDomain.CurrentDomain.GetAssemblies());

        mock.Setup(x => x.GetNamedSize(It.IsAny<NamedSize>(), It.IsAny<Type>(), It.IsAny<bool>()))
            .Returns((NamedSize size, Type targetElement, bool useOldSizes) =>
            {
                switch (size)
                {
                    case NamedSize.Default:
                        return 10;
                    case NamedSize.Micro:
                        return 4;
                    case NamedSize.Small:
                        return 8;
                    case NamedSize.Medium:
                        return 12;
                    case NamedSize.Large:
                        return 16;
                    default:
                        throw new ArgumentOutOfRangeException("size");
                }
            });

        mock.Setup(x => x.StartTimer(It.IsAny<TimeSpan>(), It.IsAny<Func<bool>>()))
            .Callback((TimeSpan interval, Func<bool> callback) =>
            {
                Timer timer = null;
                TimerCallback onTimeout = o => 
                {
                    if (callback())
                        return;

                    timer.Dispose();
                };
                timer = new Timer(onTimeout, null, interval, interval);
            });

        Device.PlatformServices = mock.Object;
        Device.SetIdiom(TargetIdiom.Desktop);
        Accessor.SetDesignMode(true);
        DependencyService.Register<SystemResourcesProvider>();
    }

    class SystemResourcesProvider : ISystemResourcesProvider
    {
        IResourceDictionary resources = new Mock<IResourceDictionary> { DefaultValue = DefaultValue.Mock }.Object;

        public IResourceDictionary GetSystemResources() => resources;
    }

    class TestTicker : Ticker
    {
        bool enabled;

        protected override void EnableTimer()
        {
            enabled = true;
            while (enabled)
                SendSignals(16);
        }

        protected override void DisableTimer() => enabled = false;
    }
}