Add a skipped test UsingExternalAliasesForHiding

src/Scripting/CSharpTest/CSharpScriptingTest.csproj

@@ -61,6 +61,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="CommandLineRunnerTests.cs" />
+    <Compile Include="TestCompilationFactory.cs" />
     <Compile Include="InteractiveSessionFixtures.cs" />
     <Compile Include="InteractiveSessionTests.cs" />
     <Compile Include="ObjectFormatterTests.cs" />
@@ -77,4 +78,4 @@
     <Import Project="..\..\..\build\Targets\VSL.Imports.targets" />
     <Import Project="..\..\..\build\Targets\Roslyn.Toolsets.Xunit.targets" />
   </ImportGroup>
-</Project>
+</Project>

src/Scripting/CSharpTest/CommandLineRunnerTests.cs

@@ -14,6 +14,8 @@
 
 namespace Microsoft.CodeAnalysis.Scripting.CSharp.UnitTests
 {
+    using static TestCompilationFactory;
+
     public class CommandLineRunnerTests : TestBase
     {
         private static readonly string CompilerVersion =
@@ -44,15 +46,6 @@ private static CommandLineRunner CreateRunner(
             return new CommandLineRunner(io, compiler, CSharpScriptCompiler.Instance, CSharpObjectFormatter.Instance);
         }
 
-        private static Compilation CreateLibrary(string assemblyName, string source)
-        {
-            return CSharpCompilation.Create(
-                assemblyName,
-                new[] { SyntaxFactory.ParseSyntaxTree(source) },
-                new[] { MscorlibRef },
-                new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
-        }
-
         [Fact]
         public void Await()
         {
@@ -402,16 +395,16 @@ public void ReferenceSearchPaths1()
 ");
 
             var dir1 = Temp.CreateDirectory();
-            dir1.CreateFile("1.dll").WriteAllBytes(CreateLibrary("1", "public class C1 {}").EmitToArray());
+            dir1.CreateFile("1.dll").WriteAllBytes(CreateCompilationWithMscorlib("public class C1 {}", "1").EmitToArray());
 
             var dir2 = Temp.CreateDirectory();
-            dir2.CreateFile("2.dll").WriteAllBytes(CreateLibrary("2", "public class C2 {}").EmitToArray());
+            dir2.CreateFile("2.dll").WriteAllBytes(CreateCompilationWithMscorlib("public class C2 {}", "2").EmitToArray());
 
             var dir3 = Temp.CreateDirectory();
-            dir3.CreateFile("3.dll").WriteAllBytes(CreateLibrary("3", "public class C3 {}").EmitToArray());
+            dir3.CreateFile("3.dll").WriteAllBytes(CreateCompilationWithMscorlib("public class C3 {}", "3").EmitToArray());
 
             var dir4 = Temp.CreateDirectory();
-            dir4.CreateFile("4.dll").WriteAllBytes(CreateLibrary("4", "public class C4 {}").EmitToArray());
+            dir4.CreateFile("4.dll").WriteAllBytes(CreateCompilationWithMscorlib("public class C4 {}", "4").EmitToArray());
 
             var runner = CreateRunner(new[] { "/r:4.dll", $"/lib:{dir1.Path}", $"/libpath:{dir2.Path}", $"/libpaths:{dir3.Path};{dir4.Path}", main.Path });
 

src/Scripting/CSharpTest/InteractiveSessionTests.cs

@@ -18,6 +18,9 @@
 
 namespace Microsoft.CodeAnalysis.Scripting.CSharp.UnitTests
 {
+    using CodeAnalysis.Test.Utilities;
+    using static TestCompilationFactory;
+
     public class HostModel
     {
         public readonly int Foo;
@@ -1151,6 +1154,23 @@ public void ReferenceDirective_RelativeToBaseRoot()
             script.GetCompilation().VerifyDiagnostics();
         }
 
+        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/6015")]
+        public void UsingExternalAliasesForHiding()
+        {
+            string source = @"
+namespace N { public class C { } }
+public class D { }
+public class E { }
+";
+
+            var libRef = CreateCompilationWithMscorlib(source, "lib").EmitToImageReference();
+
+            var script = CSharpScript.Create(@"new C()", 
+                ScriptOptions.Default.WithReferences(libRef.WithAliases(new[] { "Hidden" })).WithImports("Hidden::N"));
+
+            script.Build().Verify();
+        }
+
         #endregion
 
         #region UsingDeclarations

src/Scripting/CSharpTest/TestCompilationFactory.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using Microsoft.CodeAnalysis.CSharp;
+
+namespace Microsoft.CodeAnalysis.Scripting
+{
+    internal static class TestCompilationFactory
+    {
+        // TODO: we need to clean up and refactor CreateCompilationWithMscorlib in compiler tests 
+        // so that it can be used in portable tests.
+        internal static Compilation CreateCompilationWithMscorlib(string source, string assemblyName)
+        {
+            return CSharpCompilation.Create(
+                assemblyName,
+                new[] { SyntaxFactory.ParseSyntaxTree(source) },
+                new[] { TestReferences.NetFx.v4_0_30319.mscorlib },
+                new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
+        }
+    }
+}