Sample that shows three solutions each sharing the same packages directory.
Directory structure:
/packages
/ProjectA/ProjectA.sln
/ProjectA/.nuget/NuGet.Config
/ProjectA/ProjectA/ProjectA.csproj
/ProjectB/ProjectB.sln
/ProjectB/.nuget/NuGet.Config
/ProjectB/ProjectB/ProjectB.csproj
/Tests/ProjectC/ProjectC.sln
/Tests/ProjectC/.nuget/NuGet.Config
/Tests/ProjectC/ProjectC/ProjectC.csproj
Each solution has its own .nuget/NuGet.Config file which specifies where the packages directory is.
ProjectB.sln contains two projects: ProjectA and ProjectB
ProjectC.sln contains three projects: ProjectA, ProjectB and ProjectC.