Looking for MAUI Mock Package like Xamarin.Forms.Mocks

[logeshpalani30]

Description

I'm currently working on a project using MAUI and need a mocking framework similar to Xamarin.Forms.Mocks for MAUI. However, I'm unsure if there's an equivalent library specifically designed for MAUI. Could anyone recommend an alternative or provide guidance on how to handle mocking in MAUI projects?

Public API Changes

No API Changes

Intended Use-Case

For writing test cases on View and View Model level.

[PureWeen]

@jonathanpeppers

[jonathanpeppers]

I don't think you actually need this package for MAUI, see some conversation here: jonathanpeppers/Xamarin.Forms.Mocks#76

[jsiemensLatitudegeo]

@jonathanpeppers It still feels necessary. How do you mock DeviceInfo in a test?

Also, is there a way for instantiating UI objects to not blow up in a test, when using "net8.0-windows10.0.19041.0" target framework?

[jsiemensLatitudegeo]

eg.

        [TestMethod]
        public void TestMethod1()
        {
            var label = new Label() { Text = "abc" };
        }

 Message: 
Test method TestProject2.UnitTest1.TestMethod1 threw exception: 
System.TypeInitializationException: The type initializer for 'Microsoft.Maui.Controls.VisualElement' threw an exception. ---> System.TypeInitializationException: The type initializer for 'WinRT.ActivationFactory`1' threw an exception. ---> System.Runtime.InteropServices.COMException: Class not registered (0x80040154 (REGDB_E_CLASSNOTREG))

Works fine with 'net8.0' but not 'net8.0-windows10.0.19041.0'.

Are there any internal methods in MAUI that could be used to prevent MAUI from trying to create the underlying platform UI?

[jonathanpeppers]

I would try a plain net8.0 project without the -windows10.0.19041.0 part.

[jsiemensLatitudegeo]

That would work for this particular test, but I have a nuget package dependency that does not support net8.0. Only 'net8.0-windows10.0.19041.0', 'net8.0-ios', and 'net8.0-android'.

[FreakyAli]

Honestly i don't see it happening this soon, for the mean time you could checkout https://github.com/dotnet/maui/blob/main/src/Controls/tests/Core.UnitTests/ContentViewUnitTest.cs

[Moes81]

I really think this is a really big drawback of Maui. Not being able to mock a DeviceInfo, even IDeviceInfo, or a PermissionResult just feels anachronistic. The need of setting up an emulator in the pipeline just to test simple services, just because an IDeviceInfo is injected or another mock returns a PermissionResult leaves me speechless. I start to understand why Flutter is popular. The developer experience is just so much smoother.

[jsiemensLatitudegeo]

@jonathanpeppers The point is that changing the idiom changes the behavior of the code under test. Effectively, the code under test does something like:

 if (DeviceInfo.Idiom == Desktop) 
{ 
   // do something
} else {
  // do something else
}

The point is that we need to be able to set the idiom in the test in order to test the expected behavior.

[jonathanpeppers]

What I would do for now is call this method with System.Reflection:

maui/src/Essentials/src/DeviceInfo/DeviceInfo.shared.cs

Lines 122 to 123 in c745e23

	internal static void SetCurrent(IDeviceInfo? implementation) =>
	currentImplementation = implementation;

IDeviceInfo is public and from essentials, so seems like this should work?

Xamarin.Forms.Mocks didn't have any support for Xamarin.Essentials, and essentials was folded into MAUI.

[jsiemensLatitudegeo]

Yes, that will work. Thanks!

[Moes81]

What about using Moq to mock the state of IDeviceInfo? If I do this, i.e. new Mock<IDeviceInfo>().Setup(m => m.Platform).Returns(DevicePlatform.Android), NUnit says "Inconclusive: Test has not run". Any ideas?

[Moes81]

Okay, found my problem. This guy on stackoverflow had the exact same issue:
https://stackoverflow.com/questions/72755718/all-tests-are-inconclusive-with-the-same-an-assembly-specified-in-the-applicati

[Xyncgas]

ChatGPT is basically the same thing

[thomasgalliker]

I came across this discussion when I tried to unit test behaviors (namely, behaviors that attach to ListView). Unit testing requires some extra effor in .NET MAUI apps. To summarize some important points:

• Try to avoid access to static services (e.g. DeviceInfo.Current). Many .NET MAUI sample apps do this - which is probabyl for the sake of simplicity. But when it comes to testing, it's really bad practice! Instead, inject IDeviceInfo into your consumer classes (could be a view model or another service). Register IDeviceInfo in MauiProgram as a singleton dependency.
• Create a unit test project which targets net8.0 (not net8.0-android nor -ios nor -windows). Platform-independent code is tested in a platform-independet unit test project. Have a look at this sample project.
• When you want to test UI related stuff, things become a bit more tricky in .NET MAUI. Example: I want to test if a behavior runs correctly when it's attached to a ListView. In order to achieve this, I had to create and inject a bunch of mock objects to satisfy some MAUI interfaces. I'm sharing this code here and in this nuget package: https://www.nuget.org/packages/Mocks.Maui

Furthermore, have a look at how the MAUI guys test their own stuff and how the CommunityToolkit.Maui guys test their stuff: They replace a lot of dependencies with mock objects before they run their test code.

[Xyncgas]

Better to find these things out before working on it maybe we need a forum specifically for industrial technologies free of moderation from the people who made the technology

[ajsuydam]

I've come across this as I'm trying to write a simple unit test for my view model that uses the WeakReferenceMessenger and the Maui.Storage.FileSystem functionality. I also have other view models that have Observable properties that break under unit tests with errors that are thrown by INotifyPropertyChanged not having its dependencies met.

When using the net8.0 I get an error for the first view model that tells me I need to reference the assembly because it isn't included in the portable binary. I've spent probably three hours at this point researching this and have gotten nowhere.

For reference, what I have tried so far:

• The process outlined by Gerald Versluis in his youtube video on the subject.
• Referenced Unit test projects can't reference Maui multi target projects #3552 and several other discussions
• Tried targeting net8.0-windows10.0.19041
• Adding explicit references to the packages I need

Could someone point me in the right direction? This is my company's first try with MAUI, a lot is riding on this succeeding.