Add test for roll-forward assembly-loading behavior

src/Tests/Microsoft.NET.Publish.Tests/GivenThatAPublishedDepsJsonShouldContainVersionInformation.cs

@@ -5,6 +5,7 @@
 using System.Runtime.CompilerServices;
 using System.Text;
 using FluentAssertions;
+using Microsoft.DotNet.Cli.Utils;
 using Microsoft.Extensions.DependencyModel;
 using Microsoft.NET.TestFramework;
 using Microsoft.NET.TestFramework.Assertions;
@@ -132,5 +133,92 @@ private void Versions_are_not_included(bool build, [CallerMemberName] string cal
                 runtimeFile.FileVersion.Should().BeNull();
             }
         }
+
+        [Fact]
+        public void Inbox_version_of_assembly_is_loaded_over_applocal_version()
+        {
+            var testProject = GetTestProject();
+
+            testProject.SourceFiles["Program.cs"] = @"
+using System;
+
+static class Program
+{
+    public static void Main()
+    {
+        Console.WriteLine(typeof(object).Assembly.Location);
+        Console.WriteLine(typeof(System.Collections.Immutable.ImmutableList).Assembly.Location);
+    }
+}
+";
+
+            var testAsset = _testAssetsManager.CreateTestProject(testProject)
+                .Restore(Log, testProject.Name);
+
+            var publishCommand = new PublishCommand(Log, Path.Combine(testAsset.TestRoot, testProject.Name));
+
+            publishCommand.Execute()
+                .Should()
+                .Pass();
+
+            var publishDirectory = publishCommand.GetOutputDirectory(testProject.TargetFrameworks, runtimeIdentifier: testProject.RuntimeIdentifier);
+
+
+            //  Assembly from package should be deployed, as it is newer than the in-box version for netcoreapp2.0,
+            //  which is what the app targets
+            publishDirectory.Should().HaveFile("System.Collections.Immutable.dll");
+
+            var exePath = Path.Combine(publishDirectory.FullName, testProject.Name + ".dll");
+
+            //  We want to test a .NET Core 2.0 app rolling forward to .NET Core 2.1.
+            //  This wouldn't happen in our test environment as we also have the .NET Core 2.0 shared
+            //  framework installed.  So we get the RuntimeFrameworkVersion of an app
+            //  that targets .NET Core 2.1, and then use the --fx-version parameter to the host
+            //  to force the .NET Core 2.0 app to run on that version
+            string rollForwardVersion = GetRollForwardNetCoreAppVersion();
+
+            var foo = TestContext.Current.ToolsetUnderTest.CliVersionForBundledVersions;
+            var runAppCommand = Command.Create(TestContext.Current.ToolsetUnderTest.DotNetHostPath,
+                new string[] { "exec", "--fx-version", rollForwardVersion, exePath });
+
+            var runAppResult = runAppCommand
+                .CaptureStdOut()
+                .CaptureStdErr()
+                .Execute();
+
+            runAppResult
+                .Should()
+                .Pass();
+
+            var stdOutLines = runAppResult.StdOut.Split(Environment.NewLine);
+
+            string coreDir = Path.GetDirectoryName(stdOutLines[0]);
+            string immutableDir = Path.GetDirectoryName(stdOutLines[1]);
+
+            immutableDir.Should().BeEquivalentTo(coreDir, "immutable collections library from Framework should win");
+
+        }
+
+        string GetRollForwardNetCoreAppVersion()
+        {
+            var testProject = new TestProject()
+            {
+                Name = nameof(GetRollForwardNetCoreAppVersion),
+                TargetFrameworks = "netcoreapp2.1",
+                IsSdkProject = true,
+                IsExe = true
+            };
+            var testAsset = _testAssetsManager.CreateTestProject(testProject)
+                .Restore(Log, testProject.Name);
+            var getValuesCommand = new GetValuesCommand(Log, Path.Combine(testAsset.TestRoot, testProject.Name),
+                        testProject.TargetFrameworks, "RuntimeFrameworkVersion")
+            {
+                ShouldCompile = false
+            };
+
+            getValuesCommand.Execute().Should().Pass();
+
+            return getValuesCommand.GetValues().Single();
+        }
     }
 }