We had a bug where the framework for design time runs of dotnet test was hard coded into dnxcore50. Moved some things around so that we will pack the target framework from the project context.

test/dotnet-test.UnitTests/GivenATestRunner.cs

@@ -40,7 +40,7 @@ namespace Microsoft.Dotnet.Tools.Test.Tests
             _commandFactoryMock.Setup(c => c.Create(
                 $"dotnet-{_runner}",
                 _testRunnerArguments,
-                new NuGetFramework("DNXCore", Version.Parse("5.0")),
+                null,
                 null)).Returns(_commandMock.Object).Verifiable();
         }