Fix ROSLYN_COMPILER_LOCATION test

Author: lbussell

tests/Microsoft.DotNet.Framework.Docker.Tests/ImageDescriptor.cs

@@ -8,10 +8,6 @@ public class ImageDescriptor
     {
         public string Version { get; set; }
         public string OsVariant { get; set; }
-
-        public string GetDockerfilePath(string imageType) =>
-            $"src/{imageType}/{Version}/{OsVariant}";
-
         public string SdkVersion { get; set; }
     }
 }

tests/Microsoft.DotNet.Framework.Docker.Tests/ImageDescriptorExtensions.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Microsoft.DotNet.Framework.Docker.Tests;
+
+internal static class ImageDescriptorExtensions
+{
+    /// <summary>
+    /// The path to the Dockerfile that was used to build the image.
+    /// </summary>
+    /// <param name="imageType">"sdk", "runtime", "aspnet", or "wcf".</param>
+    public static string GetDockerfilePath(this ImageDescriptor imageDescriptor, string imageType) =>
+        $"src/{imageType}/{imageDescriptor.Version}/{imageDescriptor.OsVariant}";
+
+    /// <summary>
+    /// The expected Visual Studio installation path inside the image.
+    /// </summary>
+    public static string GetExpectedVsInstallationPath(this ImageDescriptor imageDescriptor) =>
+        imageDescriptor.OsVariant switch
+        {
+            // Visual Studio 2026/dev18 does not support Windows Server 2016.
+            // See https://learn.microsoft.com/visualstudio/releases/2026/compatibility
+            OsVersion.WSC_LTSC2016 => @"C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools",
+            _ =>                      @"C:\Program Files (x86)\Microsoft Visual Studio\18\BuildTools",
+        };
+}

tests/Microsoft.DotNet.Framework.Docker.Tests/SdkOnlyImageTests.cs

@@ -72,13 +72,14 @@ public void VerifyEnvironmentVariables(ImageDescriptor imageDescriptor)
         {
             Skip.If(IsSkippable(imageDescriptor));
 
-            List<EnvironmentVariableInfo> variables = new List<EnvironmentVariableInfo>();
+            string vsPath = imageDescriptor.GetExpectedVsInstallationPath();
 
-            variables.AddRange(RuntimeOnlyImageTests.GetEnvironmentVariables(imageDescriptor));
-
-            variables.Add(new EnvironmentVariableInfo("ROSLYN_COMPILER_LOCATION",
-                @"C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\MSBuild\Current\Bin\Roslyn"));
-            variables.Add(new EnvironmentVariableInfo("DOTNET_GENERATE_ASPNET_CERTIFICATE", "false"));
+            List<EnvironmentVariableInfo> variables =
+            [
+                ..RuntimeOnlyImageTests.GetEnvironmentVariables(imageDescriptor),
+                new EnvironmentVariableInfo("ROSLYN_COMPILER_LOCATION", $@"{vsPath}\MSBuild\Current\Bin\Roslyn"),
+                new EnvironmentVariableInfo("DOTNET_GENERATE_ASPNET_CERTIFICATE", "false"),
+            ];
 
             if (imageDescriptor.OsVariant != OsVersion.WSC_LTSC2016 &&
                 imageDescriptor.OsVariant != OsVersion.WSC_LTSC2019)
@@ -106,16 +107,7 @@ public void VerifyVsWhereOperability(ImageDescriptor imageDescriptor)
             JArray json = (JArray)JsonConvert.DeserializeObject(output);
 
             Assert.Single(json);
-
-            string expectedPath = imageDescriptor.OsVariant switch
-            {
-                // Visual Studio 2026/dev18 does not support Windows Server 2016.
-                // See https://learn.microsoft.com/visualstudio/releases/2026/compatibility
-                OsVersion.WSC_LTSC2016 => @"C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools",
-                _ =>                      @"C:\Program Files (x86)\Microsoft Visual Studio\18\BuildTools",
-            };
-
-            Assert.Equal(expectedPath, json[0]["installationPath"]);
+            Assert.Equal(imageDescriptor.GetExpectedVsInstallationPath(), json[0]["installationPath"]);
 
             // Get build version instead of a display version or semantic version because it's easier to parse and can
             // also seamlessly work with preview versions.