Add unit test verifying dockerfile aligns with current target framework (#19445)

* Add unit test verifying dockerfile aligns with current target framework.

* Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

tests/Umbraco.Tests.UnitTests/Umbraco.Templates/DockerFileTests.cs

@@ -0,0 +1,54 @@
+// Copyright (c) Umbraco.
+// See LICENSE for more details.
+
+using System.Reflection;
+using System.Runtime.Versioning;
+using NUnit.Framework;
+
+namespace Umbraco.Cms.Tests.UnitTests.Umbraco.Web.Website;
+
+[TestFixture]
+public class DockerFileTests
+{
+    [Test]
+    public void DockerFile_AspNet_Version_Matches_Target_Framework()
+    {
+        var targetFrameworkVersion = GetNetVersionFromCurrentTargetFramework();
+        (string dockerFileAspNetVersion, string dockerFileSdkVersion) = GetNetVersionsFromDockerFile();
+        Assert.AreEqual(dockerFileAspNetVersion, dockerFileSdkVersion);
+        Assert.AreEqual(targetFrameworkVersion, dockerFileAspNetVersion);
+    }
+
+    private static string GetNetVersionFromCurrentTargetFramework()
+    {
+        var targetFrameworkAttribute = Assembly.GetExecutingAssembly()
+            .GetCustomAttributes(typeof(TargetFrameworkAttribute), false)
+            .SingleOrDefault() as TargetFrameworkAttribute;
+        Assert.IsNotNull(targetFrameworkAttribute);
+
+        return targetFrameworkAttribute.FrameworkName.Replace(".NETCoreApp,Version=v", string.Empty);
+    }
+
+    private static (string DockerFileAspNetVersion, string DockerFileSdkVersion) GetNetVersionsFromDockerFile()
+    {
+        const int SegmentsToRepoRoot = 5; // Number of directory segments from the test directory to the repository root.
+        var testContextDirectoryParts = TestContext.CurrentContext.TestDirectory.Split(Path.DirectorySeparatorChar);
+        var solutionRootDirectory = string.Join(Path.DirectorySeparatorChar, testContextDirectoryParts.Take(testContextDirectoryParts.Length - SegmentsToRepoRoot));
+        var dockerFilePath = Path.Combine(solutionRootDirectory, "templates", "UmbracoProject", "Dockerfile");
+
+        var dockerFileContent = File.ReadAllText(dockerFilePath);
+        var dockerFileFromLines = dockerFileContent
+            .Split(Environment.NewLine, StringSplitOptions.RemoveEmptyEntries)
+            .Where(x => x.StartsWith("FROM mcr."))
+            .ToList();
+
+        Assert.AreEqual(2, dockerFileFromLines.Count);
+
+        var dockerFileAspNetVersion = GetVersionFromDockerFromLine(dockerFileFromLines[0]);
+        var dockerFileSdkVersion = GetVersionFromDockerFromLine(dockerFileFromLines[1]);
+
+        return (dockerFileAspNetVersion, dockerFileSdkVersion);
+    }
+
+    private static string GetVersionFromDockerFromLine(string line) => line.Split(' ')[1].Split(':')[1];
+}