Right, it's used to limit parallelization across projects:  https://github.com/dotnet/aspnetcore/blob/52eff90fbcfca39b7eb58baad597df6a99a542b0/src/SignalR/Directory.Build.targets#L5-L6    I don't think you'd want any of these IIS tests running in parallel since they interact with the global IIS service, so they should all be in unique groups.