How can I get NUnit3TestAdapter to work with .Net Standard 2.0?

I receive the following error:

1>C:\Nikeza\Mobile\Nikeza.Mobile\Tests\ExampleBased.fsproj :

warning NU1701: Package 'NUnit3TestAdapter 3.9.0' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETStandard,Version=v2.0'.

This package may not be fully compatible with your project. 1>ExampleBased -> C:\Nikeza\Mobile\Nikeza.Mobile\Tests\bin\Debug\netstandard2.0\ExampleBased.dll

Solution

You don't provide enough information to diagnose what is wrong with your project file, but it 3.9.0 of the NUnit Adapter does work with .NET Standard 2.0 and F#. I think that your test project is targeting .NET Standard. It needs to target .NET Core or .NET 4.6.1+. Test projects are treated like executables, they need to target a specific framework, not .NET Standard. The code that you are testing can be .NET Standard though.

You should follow the documentation Unit testing F# libraries in .NET Core using dotnet test and NUnit and read the NUnit docs, .NET Core and .NET Standard.

Your project file should look something like this,

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netcoreapp2.0</TargetFramework>

    <IsPackable>false</IsPackable>
  </PropertyGroup>

  <ItemGroup>
    <Compile Include="Tests.fs" />
    <Compile Include="Program.fs" />
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
    <PackageReference Include="NUnit" Version="3.9.0" />
    <PackageReference Include="NUnit3TestAdapter" Version="3.9.0" />
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\MathService\MathService.fsproj" />
  </ItemGroup>

</Project>