Update MSTest template.json to create dotnet.config (#50482)

Author: Youssef1313

template_feed/Microsoft.DotNet.Common.ProjectTemplates.10.0/content/MSTest-CSharp/.template.config/template.json

@@ -227,6 +227,19 @@
       "id": "restoreNugetPackages",
       "continueOnError": true
     },
+    {
+      "condition": "(TestRunner == \"Microsoft.Testing.Platform\")",
+      "description": "Create or update 'dotnet.config' file required by Microsoft.Testing.Platform.",
+      "manualInstructions": [{ "text": "Manually create 'dotnet.config' file setting the test runner to Microsoft.Testing.Platform" }],
+      "actionId": "597E7933-0D87-452C-B094-8FA0EEF7FD97",
+      "id": "createOrUpdateDotnetConfig",
+      "args": {
+        "section": "dotnet.test.runner",
+        "key": "name",
+        "value": "Microsoft.Testing.Platform",
+      },
+      "continueOnError": true
+    },
     {
       "condition": "(HostIdentifier != \"dotnetcli\" && HostIdentifier != \"dotnetcli-preview\")",
       "description": "Opens Test1.cs in the editor",

template_feed/Microsoft.DotNet.Common.ProjectTemplates.10.0/content/MSTest-FSharp/.template.config/template.json

@@ -227,6 +227,19 @@
       "id": "restoreNugetPackages",
       "continueOnError": true
     },
+    {
+      "condition": "(TestRunner == \"Microsoft.Testing.Platform\")",
+      "description": "Create or update 'dotnet.config' file required by Microsoft.Testing.Platform.",
+      "manualInstructions": [{ "text": "Manually create 'dotnet.config' file setting the test runner to Microsoft.Testing.Platform" }],
+      "actionId": "597E7933-0D87-452C-B094-8FA0EEF7FD97",
+      "id": "createOrUpdateDotnetConfig",
+      "args": {
+        "section": "dotnet.test.runner",
+        "key": "name",
+        "value": "Microsoft.Testing.Platform",
+      },
+      "continueOnError": true
+    },
     {
       "condition": "(HostIdentifier != \"dotnetcli\" && HostIdentifier != \"dotnetcli-preview\")",
       "description": "Opens Test1.fs in the editor",

template_feed/Microsoft.DotNet.Common.ProjectTemplates.10.0/content/MSTest-VisualBasic/.template.config/template.json

@@ -227,6 +227,19 @@
       "id": "restoreNugetPackages",
       "continueOnError": true
     },
+    {
+      "condition": "(TestRunner == \"Microsoft.Testing.Platform\")",
+      "description": "Create or update 'dotnet.config' file required by Microsoft.Testing.Platform.",
+      "manualInstructions": [{ "text": "Manually create 'dotnet.config' file setting the test runner to Microsoft.Testing.Platform" }],
+      "actionId": "597E7933-0D87-452C-B094-8FA0EEF7FD97",
+      "id": "createOrUpdateDotnetConfig",
+      "args": {
+        "section": "dotnet.test.runner",
+        "key": "name",
+        "value": "Microsoft.Testing.Platform",
+      },
+      "continueOnError": true
+    },
     {
       "condition": "(HostIdentifier != \"dotnetcli\" && HostIdentifier != \"dotnetcli-preview\")",
       "description": "Opens Test1.vb in the editor",

template_feed/Microsoft.DotNet.Common.ProjectTemplates.10.0/content/Playwright-MSTest-CSharp/.template.config/template.json

@@ -247,6 +247,19 @@
       "id": "restoreNugetPackages",
       "continueOnError": true
     },
+    {
+      "condition": "(TestRunner == \"Microsoft.Testing.Platform\")",
+      "description": "Create or update 'dotnet.config' file required by Microsoft.Testing.Platform.",
+      "manualInstructions": [{ "text": "Manually create 'dotnet.config' file setting the test runner to Microsoft.Testing.Platform" }],
+      "actionId": "597E7933-0D87-452C-B094-8FA0EEF7FD97",
+      "id": "createOrUpdateDotnetConfig",
+      "args": {
+        "section": "dotnet.test.runner",
+        "key": "name",
+        "value": "Microsoft.Testing.Platform",
+      },
+      "continueOnError": true
+    },
     {
       "condition": "(HostIdentifier != \"dotnetcli\" && HostIdentifier != \"dotnetcli-preview\")",
       "description": "Opens Test1.cs in the editor",

test/dotnet-new.IntegrationTests/DotnetNewTestTemplatesTests.cs

@@ -180,6 +180,10 @@ public void MSTestAndPlaywrightProjectTemplate_WithCoverageToolAndTestRunner_Can
         {
             string testProjectName = GenerateTestProjectName();
             string outputDirectory = CreateTemporaryFolder(folderName: "Home");
+
+            // Prevent the dotnet.config post action from walking up the directory parents up to our own solution root, which would affect other tests.
+            Directory.CreateDirectory(Path.Combine(outputDirectory, ".git"));
+
             string workingDirectory = CreateTemporaryFolder();
 
             // Create new test project: dotnet new <projectTemplate> -n <testProjectName> -f <targetFramework> -lang <language> --coverage-tool <coverageTool> --test-runner <testRunner>
@@ -196,10 +200,7 @@ public void MSTestAndPlaywrightProjectTemplate_WithCoverageToolAndTestRunner_Can
                 var isMTP = testRunner == "Microsoft.Testing.Platform";
                 if (isMTP)
                 {
-                    File.WriteAllText(Path.Combine(outputDirectory, "dotnet.config"), """
-                        [dotnet.test.runner]
-                        name = "Microsoft.Testing.Platform"
-                        """);
+                    File.Exists(Path.Combine(outputDirectory, "dotnet.config")).Should().BeTrue();
                 }
 
                 var result = new DotnetTestCommand(_log, false)