How do I mock an application (in English, if possible)

[mdelgadov]

I'm trying to test properly, not only existence but also behavior.
Frequently, I need to interact with the Application objects.

For example, I need to test that an entry triggers the Unfocused event:

 [Fact]
 public void InsertBehaviorUnfocused_ShouldAttachUnfocusedEvent()
 {
     // Arrange
     var view = new Entry();
     var commandMock = new Mock<ICommand>();
     commandMock.Setup(cmd => cmd.Execute(It.IsAny<object>())).Verifiable();
    view.Focus();
    view.Unfocus();
    
    commandMock.Verify(cmd => cmd.Execute(It.IsAny<object>()), Times.Once);
    Assert.Same(view, result);
}

The test fails because the event doesn't trigger in the vacuum. The entry needs to be part of a view tree which means, an app, a window, a page and finally, my entry.

I haven't found any written support at all. This seems a regular case, doesn't it? Nobody tests if the event has been triggered and other activities?

Going further, I went to the mother of the deep rabbit holes, the Github Microsoft Maui repository, and find many tests involving an app.

For example:

[Fact]
public void SettingMainPageSetsMainPageButNotWindow()
{
	var app = new Application();
	var page = new ContentPage();

	app.MainPage = page;

	Assert.Equal(page, app.MainPage);
	Assert.Empty(app.Windows);
}

It became very confusing because there is not a proper set of requirements. For example, how deep it goes when the fixture constructor does this:

public class BaseTestFixture : IDisposable
{
	CultureInfo _defaultCulture;
	CultureInfo _defaultUICulture;

	public BaseTestFixture()
	{
		Microsoft.Maui.Controls.Hosting.CompatibilityCheck.UseCompatibility();
		_defaultCulture = System.Threading.Thread.CurrentThread.CurrentCulture;
		_defaultUICulture = System.Threading.Thread.CurrentThread.CurrentUICulture;
		DispatcherProvider.SetCurrent(new DispatcherProviderStub());
		DeviceDisplay.SetCurrent(null);
		DeviceInfo.SetCurrent(null);
		AppInfo.SetCurrent(null);
	}

I simply don't know how and what are the implications of such code.

There are many other stubs and mocks, but I've had similar issues.

So, I have two questions:

1. Is there any documentation about mocking Maui Apps and its properties?

2. How do I test around code that contains App and other references, like:

if (header is not null && App.Current.Resources.TryGetValue(...

I can always use wrappers, but doesn't that is just kinking the can down the street?

Thanks in advance.
Miguel Delgado