How to get nUnit unit tests to work with Xamarin.Forms in Azure pipelines?

Question

I'm trying to get nUnit unit tests working with Xamarin.Forms. Everything works fine on my machine, but when I push to Azure and it goes into the build pipeline, I get the following error :

The current .NET SDK does not support targeting .NET Core 3.1. Either target .NET Core 2.2 or lower, or use a version of the .NET SDK that supports .NET Core 3.1 [/Users/runner/runners/2.164.6/work/1/s/TestProject1/TestProject1.csproj

When I remove the unit test project, the build is successful. I think the problem has something to do with the fact that Xamarin.Forms uses .Net Standard, while my unit test project is using .NET Core. How do I reconcile this? Specific advice or a pointer to a tutorial that goes over unit testing with Xamarin.Forms on Azure would be greatly appreciated. I'm really new to playing around with devops, so some kind of training track would be nice.

Also, here is my Azure Pipeline YAML file :

    pool:
      vmImage: 'macOS 10.13'

    steps:
      # To manually select a Xamarin SDK version on the Hosted macOS agent, enable this script with the SDK version you want to target
      # https://go.microsoft.com/fwlink/?linkid=871629
      - script: sudo $AGENT_HOMEDIRECTORY/scripts/select-xamarin-sdk.sh 5_4_1
        displayName: 'Select Xamarin SDK version'
        enabled: false

      - task: NuGetToolInstaller@0

      - task: NuGetCommand@2
        inputs:
          restoreSolution: '**/*.sln'

      - task: XamariniOS@2
        inputs:
          solutionFile: '**/*.sln'
          configuration: 'Release'
          buildForSimulator: true
          packageApp: false 

Thanks!

Answer 1

As you already mentioned the unit test project is a .NET Core project and thus has to be executed with .NET Core. In a YAML build definition you can do this as follows:

- task: UseDotNet@2
  displayName: 'Install .NET Core SDK'
  inputs:
    version: 3.1.x
    performMultiLevelLookup: true

- task: DotNetCoreCLI@2
  displayName: Build Tests
  inputs:
    command: 'build'
    projects: '**\*Test.csproj'
    arguments: '--configuration Release'

- task: DotNetCoreCLI@2
  displayName: Run Tests
  inputs:
    command: 'test'
    projects: '**\*Test.csproj'
    arguments: '--configuration Release'

Here an example of a complete build pipeline definition to build a Xamarin Forms application with unit tests:

trigger:
  branches:
    include:
    - '*'

pool:
  vmImage: 'windows-2019'

steps:
- task: NuGetToolInstaller@0
  displayName: Instal Nuget
  inputs:
    checkLatest: true

- task: NuGetCommand@2
  displayName: Restore Nuget Packages
  inputs:
    restoreSolution: '**/*.sln'

- task: UseDotNet@2
  displayName: 'Install .NET Core SDK'
  inputs:
    version: 3.1.x
    performMultiLevelLookup: true

- task: DotNetCoreCLI@2
  displayName: Build Tests
  inputs:
    command: 'build'
    projects: '**\*Test.csproj'
    arguments: '--configuration Release'

- task: DotNetCoreCLI@2
  displayName: Run Tests
  inputs:
    command: 'test'
    projects: '**\*Test.csproj'
    arguments: '--configuration Release'

- task: XamarinAndroid@1
  displayName: Build Android App
  inputs:
    projectFile: '**/*Android*.csproj'
    outputDirectory: '$(build.binariesDirectory)/Release'
    configuration: 'Release'

Guess the answer is a little too late for combodev1, but maybe it helps someone else who ends up here.