Create unit-testing-mstest-migration-from-v1-to-v3.md.md

Author: engyebrahim

docs/core/testing/unit-testing-mstest-migration-from-v1-to-v3.md.md

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+# MSTest v3 Migration Guide
+
+## Overview
+This guide assists users in upgrading their MSTest projects from v0/v1 to MSTest v3. MSTest v3 introduces new features, improvements, and some breaking changes.
+
+---
+
+## Introduction and Motivation
+
+Migrating to MSTest v3 offers several benefits:
+- Improved test execution speeds and memory efficiency.
+- Stricter validation for more reliable tests.
+- Leveraging modern .NET features and cross-platform compatibility.
+
+---
+
+## Steps to Migrate
+
+### 1. Remove Assembly Reference
+Remove the `Microsoft.VisualStudio.QualityTools.UnitTestFramework` reference from your project.
+
+```xml
+<Reference Include="Microsoft.VisualStudio.QualityTools.UnitTestFramework, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
+    <Private>False</Private>
+</Reference>
+```
+
+### 2. Update Your Project
+- **NuGet Package**: Install the latest [MSTest](https://www.nuget.org/packages/MSTest).
+- **Project File**: Update your project file to use MSTest SDK.
+
+```xml
+<Project Sdk="MSTest.Sdk/3.3.1">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+</Project>
+```
+
+### 3. Update Your Code
+- **Replace Deprecated Methods**: Update deprecated methods to newer versions.
+  - `Assert.AreEqual/AreNotEqual` (with object) → Use generic versions.
+  - `Assert.AreSame/AreNotSame` (with object) → Use generic versions.
+- **Test Initialization**: Use `TestInitialize` methods for async initialization.
+- **Cleanup**: Use `TestCleanup` methods or the `Dispose` pattern for cleanup.
+- **RunSettings**: The `.testsettings` file is no longer supported, meaning `<LegacySettings>` is also no longer available. Use [.runsettings](https://learn.microsoft.com/en-gb/visualstudio/test/configure-unit-tests-by-using-a-dot-runsettings-file?view=vs-2022) for test configuration.
+
+---
+
+## New Features in MSTest v3
+
+- Improved defaults for test projects
+- Simplified setup and usage
+- Enhanced extensibility of the MSTest runner
+- New Roslyn-based code analyzers for improved test development
+- Support for WinUI applications
+- In-assembly parallel execution
+- Dynamic data sources for data-driven tests
+
+---
+
+## Deprecated Features
+
+- Dropped support for:
+  - **.NET Framework 4.5** (use .NET 4.6.2 or higher)
+  - **.NET Standard 1.0** (use .NET Standard 2.0)
+  - **UWP versions before 16299**
+  - **WinUI versions before 18362**
+  - **.NET 5** (use .NET Core 3.1 or .NET 6)
+
+---
+
+## Breaking Changes and Removed APIs
+
+### Assertion Overloads
+MSTest v3 removes certain `Assert` overloads that accept object types to promote type-safe assertions. Update tests using these overloads to specify types explicitly.
+
+**Example**:
+
+```csharp
+// Old (v0/v1)
+Assert.AreEqual(expected, actual); // both are objects
+
+// New (v3)
+Assert.AreEqual<int>(expectedInt, actualInt); // specify the type
+```
+
+### DataRowAttribute Updates
+The `DataRowAttribute` constructors have been simplified in MSTest v3. Update parameterized tests using `DataRow` to align with the revised constructors.
+
+**Example**:
+
+```csharp
+[TestMethod]
+[DataRow(1, "test")]
+public void MyTestMethod(int number, string text) { ... }
+```
+
+### Timeout Settings
+Timeout settings are standardized across frameworks in MSTest v3. Verify and adjust any timeout configurations in existing tests for compatibility.
+
+---
+
+## Configuration Changes
+
+### Settings and Configuration Files
+MSTest v3 supports both XML and JSON formats for configuration files.
+
+1. **Verify Configurations**: Ensure that existing `.runsettings` files align with MSTest v3’s syntax and structure.
+2. **Convert to JSON (if applicable)**: For JSON-based configurations, convert XML settings to JSON format.
+
+---
+
+## Parallel Execution and Performance Optimization
+
+### New Parallelism Options
+Configure parallel execution in `.runsettings` or JSON configuration files to improve performance.
+
+**Example**:
+
+```json
+{
+  "RunConfiguration": {
+    "MaxCpuCount": -1 // Uses all available processors
+  }
+}
+```
+
+### Improved Resource Usage
+MSTest v3 optimizes resource management, resulting in lower memory usage and better CPU efficiency.
+
+---
+
+## Handling Obsolete Attributes and Migrating Custom Extensions
+Review deprecated attributes, such as `[DeploymentItem]`, and replace them with MSTest v3 alternatives where possible.
+
+---
+
+## Code Analyzers and Best Practices
+MSTest v3 includes built-in code analyzers for best practices, avoiding configuration pitfalls, and proper use of MSTest attributes and settings.
+
+---
+
+## Sample Code: Migration Example
+
+### Before (MSTest v1)
+```csharp
+[TestMethod]
+[Timeout(1000)]
+[DataRow(1, "data")]
+public void ExampleTestMethod(int number, string data) {
+    Assert.AreEqual(number, Convert.ToInt32(data));
+}
+```
+
+### After (MSTest v3)
+```csharp
+[TestMethod]
+[Timeout(1000)]
+[DataRow(1, "data")]
+public void ExampleTestMethod(int number, string data) {
+    Assert.AreEqual<int>(number, Convert.ToInt32(data));
+}
+