Microsoft.CSharp.Core.targets missing

In my case, opening the existing Solution file (with .sln extension), it installed all the missing dependencies.

Otherwise check for missing target packages at nuget.org manually and install them (e.g. MSBuild.Microsoft.VisualStudio.Web.targets).

As per this GitHub issue, you'll need to set $(RoslynTargetsPath).

If MSBuild is installed on the machine and your tests run in a Visual Studio Developer Command Prompt, then you shouldn't need to do anything. However, MSBuild 15.0 no longer places itself in the registry which makes it impossible for MSBuild to find itself. This is because of a mandate by Visual Studio where you can have multiple side-by-side installations. MSBuild in this case would be installed once per Visual Studio instance. MSBuild now finds itself by looking at environment variables set by the VS command prompt.

If you want to fully redistribute MSBuild via a combination of our packages and all of the other packages needed to do full project evaluation, you will have to set RoslynTargetsPath before you load projects. You could argue this is an issue with NuGet since all packages' <contentFiles /> go to the the root of your output directory and you can't specify a subdirectory for certain packages.