Fix VS version test

Author: lbussell

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

@@ -20,18 +20,30 @@ public static class Config
             Environment.GetEnvironmentVariable("DOCKERFILE_PATHS")?
                 .Split(',', StringSplitOptions.RemoveEmptyEntries) ?? Array.Empty<string>();
 
+        #nullable enable
+        private static JObject? _manifestVariables = null;
+        public static JObject ManifestVariables
+        {
+            get
+            {
+                _manifestVariables ??= GetManifestVariables();
+                return _manifestVariables;
+            }
+        }
+        #nullable disable
+
         public static string GetManifestRegistry()
         {
             string manifestJson = File.ReadAllText("manifest.json");
             JObject manifest = JObject.Parse(manifestJson);
             return (string)manifest["registry"];
         }
 
-        public static Version GetManifestVsVersion()
+        private static JObject GetManifestVariables()
         {
             string manifestJson = File.ReadAllText("manifest.versions.json");
             JObject manifest = JObject.Parse(manifestJson);
-            return System.Version.Parse((string)(manifest["variables"]["vs|version"]));
+            return (JObject)manifest["variables"];
         }
 
         public static string GetFilterRegexPattern(string filter)

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

@@ -2,6 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
+using Newtonsoft.Json.Linq;
+
 namespace Microsoft.DotNet.Framework.Docker.Tests;
 
 internal static class ImageDescriptorExtensions
@@ -13,6 +16,23 @@ internal static class ImageDescriptorExtensions
     public static string GetDockerfilePath(this ImageDescriptor imageDescriptor, string imageType) =>
         $"src/{imageType}/{imageDescriptor.Version}/{imageDescriptor.OsVariant}";
 
+    /// <summary>
+    /// The expected Visual Studio version installed inside the image.
+    /// </summary>
+    public static Version GetExpectedVsVersion(this ImageDescriptor imageDescriptor)
+    {
+        JObject manifestVariables = Config.ManifestVariables;
+        string vsVersionVariable = 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 => "vs|ltsc2016|version",
+            _ =>                      "vs|version",
+        };
+
+        return Version.Parse((string)manifestVariables[vsVersionVariable]);
+    }
+
     /// <summary>
     /// The expected Visual Studio installation path inside the image.
     /// </summary>

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

@@ -112,8 +112,7 @@ public void VerifyVsWhereOperability(ImageDescriptor imageDescriptor)
             // 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.
             Version actualVsVersion = Version.Parse(json[0]["catalog"]["buildVersion"].ToString());
-
-            Version expectedVsVersion = Config.GetManifestVsVersion();
+            Version expectedVsVersion = imageDescriptor.GetExpectedVsVersion();
 
             Assert.Equal(expectedVsVersion.Major, actualVsVersion.Major);
             Assert.Equal(expectedVsVersion.Minor, actualVsVersion.Minor);