Move package compatibility app to tools and add robust test coverage

.github/instructions/testing.instructions.md

@@ -173,6 +173,45 @@ dotnet test ... --filter "FullyQualifiedName=Namespace.ClassName.MethodName"
 
 ## Writing Tests
 
+### Test Documentation Requirements
+
+To keep tests maintainable for contributors and AI agents, test intent must be documented at
+class and method level.
+
+#### Required XML Documentation
+- Add XML `<summary>` comments to every test class.
+- Add XML `<summary>` comments to every test method (`[Fact]`, `[Theory]`, conditional variants).
+- For helper methods used by tests, add XML `<summary>` comments and XML `<param>` / `<returns>`
+  where applicable.
+- For fixture and collection types, add XML `<summary>` comments describing why the fixture exists
+  (for example, serialization of console-mutating tests).
+
+#### What the Comments Must Explain
+- The behavior/contract being tested (not just restating the method name).
+- Why the scenario matters (for example: regression guard, parsing contract, sync/async parity,
+  isolation requirement).
+- For helper methods, what side effects occur (for example console redirection, file system
+  copying, process execution) and why they are needed.
+
+#### Style Guidance
+- Keep comments concise and factual.
+- Prefer behavior-focused wording over implementation trivia.
+- Avoid comments that merely repeat obvious code.
+- Use inline comments inside test methods only for non-obvious setup/act/assert details.
+
+#### Example
+```csharp
+/// <summary>
+/// Ensures malformed connection strings return a non-zero exit code and emit a parse error
+/// without verbose exception details.
+/// </summary>
+[Fact]
+public void AppRunWithMalformedConnectionStringReturnsOneAndWritesParseError()
+{
+        // Arrange / Act / Assert
+}
+```
+
 ### Test Structure
 ```csharp
 public class FeatureNameTests

src/Microsoft.Data.SqlClient.slnx

@@ -10,9 +10,6 @@
       <Platform Solution="*|x86" Project="x86" />
     </Project>
   </Folder>
-  <Folder Name="/doc/apps/">
-    <Project Path="../doc/apps/AzureAuthentication/AzureAuthentication.csproj" />
-  </Folder>
   <Folder Name="/doc/snippets/" />
   <Folder Name="/doc/snippets/Microsoft.Data.Sql/">
     <File Path="../doc/snippets/Microsoft.Data.Sql/SqlDataSourceEnumerator.xml" />
@@ -170,7 +167,6 @@
   <Folder Name="/src/Microsoft.Data.SqlClient/src/">
     <Project Path="Microsoft.Data.SqlClient/src/Microsoft.Data.SqlClient.csproj" />
   </Folder>
-  <Folder Name="/src/Microsoft.Data.SqlClient/tests/" />
   <Folder Name="/src/Microsoft.SqlServer.Server/">
     <Project Path="Microsoft.SqlServer.Server/Microsoft.SqlServer.Server.csproj" />
   </Folder>
@@ -215,4 +211,6 @@
     <Project Path="Microsoft.Data.SqlClient/tests/ManualTests/SQL/UdtTest/UDTs/Shapes/Shapes.csproj" />
     <Project Path="Microsoft.Data.SqlClient/tests/ManualTests/SQL/UdtTest/UDTs/Utf8String/Utf8String.csproj" />
   </Folder>
+  <Project Path="../tools/PackageCompatibility/src/PackageCompatibility.csproj" />
+  <Project Path="../tools/PackageCompatibility/test/PackageCompatibility.Test.csproj" />
 </Solution>

tools/PackageCompatibility/Directory.Packages.props

@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+  <!-- We purposely do not include any parent Directory.Packages.props files. -->
+
+  <PropertyGroup>
+    <!-- Use the following package versions if not supplied. -->
+    <AbstractionsVersion>1.0.0</AbstractionsVersion>
+    <AkvProviderVersion>7.0.0</AkvProviderVersion>
+    <LoggingVersion>1.0.0</LoggingVersion>
+    <SqlClientVersion>7.0.1</SqlClientVersion>
+    <SqlServerVersion>1.0.0</SqlServerVersion>
+
+    <!-- We omit referencing the Azure package entirely by default. -->
+  </PropertyGroup>
+
+  <!-- SqlClient Packages -->
+  <ItemGroup>
+    <!--
+      Normal apps wouldn't explicitly reference these 2 packages, but we do here to force the
+      desired versions.  This helps detect version conflicts.
+    -->
+    <PackageVersion Include="Microsoft.Data.SqlClient.Extensions.Abstractions" Version="$(AbstractionsVersion)" />
+    <PackageVersion Include="Microsoft.Data.SqlClient.Internal.Logging" Version="$(LoggingVersion)" />
+
+    <!-- These are normal references for apps. -->
+    <PackageVersion Include="Microsoft.Data.SqlClient.AlwaysEncrypted.AzureKeyVaultProvider" Version="$(AkvProviderVersion)" />
+    <PackageVersion Include="Microsoft.Data.SqlClient" Version="$(SqlClientVersion)" />
+    <PackageVersion Include="Microsoft.SqlServer.Server" Version="$(SqlServerVersion)" />
+
+    <!-- Declare a version for the Azure package if one was specified. -->
+    <PackageVersion
+      Include="Microsoft.Data.SqlClient.Extensions.Azure"
+      Version="$(AzureVersion)"
+      Condition="'$(AzureVersion)' != ''" />
+  </ItemGroup>
+
+  <!-- Other Packages -->
+  <ItemGroup>
+    <PackageVersion Include="System.CommandLine" Version="2.0.6" />
+    <PackageVersion Include="xunit.v3" Version="4.0.0-pre.81" />
+  </ItemGroup>
+
+</Project>