Upgrade Tests project to .NET Core 3.1 to attempt to resolve AppVeyor failures
Upgrade Tests project to .NET Core 3.1 to attempt to resolve AppVeyor failures

JasonBock/csla,rockfordlhotka/csla,MarimerLLC/csla,JasonBock/csla,rockfordlhotka/csla,rockfordlhotka/csla,JasonBock/csla,MarimerLLC/csla,MarimerLLC/csla