Unit test projects can't reference Maui multi target projects

[JohnHDev]

Description

With the new design for multi target projects, we need to be able to unit test ViewModels stored in Maui projects.

We could move ViewModels into pure .net 6 projects, but dependencies that are defined in other multi target projects with platform specific implementations can't be mocked regardless without also moving the interfaces for those dependencies into .net 6 projects. That largely negates the positives of multi target projects if we have to create other projects just to contain the Interface definitions and view models.

Steps to Reproduce

Create a .NET Maui solution
Create a ViewModel to the .NET Maui project.
Create a unit test project and add a reference to the .NET Maui project.

Version with bug

Preview 10 (current)

Last version that worked well

Unknown/Other

Affected platforms

I was not able test on other platforms

Affected platform versions

All

Did you find any workaround?

Create another .net 6 project for view modals and interfaces that the tests and .net maui projects can reference.
That just doesn't scale well.

Relevant log output

No response

[devmikew]

Just some thoughts!

In the pure MVVM world your view models should not have references to UI components. This is so they can be unit tested!!

Which is your problem here. So what other references do you have?

Also it is possible to create another testing project which just has file links to the view models. And then run your unit tests against this.

You could also exclude other references by #if in the files and setting a TEST define in the unit test project.

[JohnHDev]

@devmikew I agree, view models should not have references to UI components. Mine don't, they just happen to live in the same project as the views. They don't have to, as I mentioned. But I like to keep views and models organised.

Then consider platform specific implementations for any dependencies that view models might need, lets say a ICalendarRepository with a concrete implementation for each platform. Lets add a Calendars Maui project with the actual platform specific code, the interface definition can also be in the same project. You can't then mock that interface in a test because I can't reference the Maui project from a test project. I can create a separate project just for the interface, but that feels like massive overkill.

[devmikew]

The ICalendarRepository seems to be a data/business layer.

Couldn't you add a net6.0 target framework for this (the repository) project and in that target framework implementation do nothing. Normally you would only target android/ios/windows in this project as these are the real runtime platforms.

[JohnHDev]

Not sure I follow your suggestion, concrete implementations of ICalendarRepository would be to access iOS EKEvents, Android calendar, Windows Appointments etc in a generic way. It isn't business logic, but it is native data access.

The platform specific implementation of ICalendarRepository is DI'ed into the VM constructor. The logic is held in the VM. The VM needs to be unit tested and I would need to mock ICalendarRepository (and any other dependencies it has). I can't though as the unit test project can't access the multi target library Maui projects.

As I said, I could move the interfaces into a .net 6 project, I just don't think I should have to.

[devmikew]

Sorry, but what I tried to say, was to provide an implementation for net-6.0. This implementation does not need to do anything except return a valid result. Get Outlook for Android<https://aka.ms/AAb9ysg>

…

________________________________ From: JohnHDev ***@***.***> Sent: Friday, November 26, 2021 9:07:31 AM To: dotnet/maui ***@***.***> Cc: devmikew ***@***.***>; Mention ***@***.***> Subject: Re: [dotnet/maui] Unit test projects can't reference Maui multi target projects (Issue #3552) Not sure I follow your suggestion, concrete implementations of ICalendarRepository would be to access iOS EKEvents, Android calendar, Windows Appointments etc in a generic way. It isn't business logic, but it is native data access. The platform specific implementation of ICalendarRepository is DI'ed into the VM constructor. The logic is held in the VM. The VM needs to be unit tested and I would need to mock ICalendarRepository (and any other dependencies it has). I can't though as the unit test project can't access the multi target library Maui projects. As I said, I could move the interfaces into a .net 6 project, I just don't think I should have to. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<#3552 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AKBBNIJ3RZD4S75USOEGJ5DUN26THANCNFSM5IZJFLGA>. Triage notifications on the go with GitHub Mobile for iOS<https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android<https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

[JohnHDev]

I am talking about mocking ICalendarRepository in a test, it has nothing to do with concrete implementations.
The issue is the Maui project cannot be referenced from the unit test project. Adding a .net 6 implementation doesn't help.

[VladislavAntonyuk]

Please see how it is implemented in Community toolkit https://github.com/CommunityToolkit/Maui/blob/main/src/CommunityToolkit.Maui.UnitTests/CommunityToolkit.Maui.UnitTests.csproj

[JohnHDev]

@VladislavAntonyuk thanks, I have updated my project to match (including removing nunit and adding xunit) but Im not seeing any difference. What is the magic ingredient with that?

[VladislavAntonyuk]

could you share your simple project to reproduce the issue? most likely you have some dependencies which cannot be resolved

[JohnHDev]

UnitTestExample.zip

Here is a very simple example, new Maui solution, added a MainPageModel, added a unit test project, added reference to the maui project in the unit test project, it is not compatible. The unit test project would contain tests for the MainPageModel but obviously can't get that far.

[VladislavAntonyuk]

I see, you try to add executable project to unit test lib. you can only add Maui Library project.

[JohnHDev]

Its a Maui project that also generates the apps, so it really should not make any difference.

Ok, so try this one:
UnitTestExample.zip

I have moved the MainPageModel into its own .net 6 project, and added a reference to an interface held in a new Maui project. It not build because .net 6 projects can't reference .net maui projects.

As I said, I can fix that by moving the ICalendarRepository into a separate .net 6 project, but we shouldn't have to.

[VladislavAntonyuk]

you are doing it wrong. you are trying to add maui library to net6.0 library. it is not correct.
the path should be:
net6.0=>maui library=>maui executable

[VladislavAntonyuk]

UnitTestExample.zip