feat(testing): migrate test infrastructure to Microsoft Testing Platform

[j-d-ha]

🚀 Pull Request

📋 Summary

This PR migrates the test infrastructure from xUnit's legacy test runner to Microsoft Testing Platform (MTP), the modern native .NET test execution framework. This migration modernizes our testing infrastructure and improves code coverage collection through native .NET tooling.

Key Changes

1. Microsoft Testing Platform Migration

   • Updated global.json to specify MTP as the test runner ("runner": "Microsoft.Testing.Platform")
   • Added Microsoft.Testing.Extensions.CodeCoverage package to all test projects
   • Replaced Coverlet with native MTP coverage collection
   • All test projects now use MTP for execution and coverage

2. Package Management Modernization

   • Normalized and aligned package references across all projects in Directory.Packages.props
   • Ensured consistent versioning for test-related dependencies
   • Cleaned up package reference structure

3. CI/CD Workflow Updates

   • Updated both main-build.yaml and pr-build.yaml workflows
   • Changed coverage collection from --collect:"XPlat Code Coverage" to --coverage --coverage-output-format cobertura
   • Updated Codecov file pattern to match new output format (*.cobertura.xml)

4. Documentation & Configuration

   • Added comprehensive test command reference to CLAUDE.md with examples for:
     • Running tests across multiple frameworks
     • Framework-specific test execution
     • Test discovery and filtering with MTP syntax (method, class, namespace)
   • Updated CONTRIBUTING.md with correct coverage command
   • Updated TestTasks.yml to use MTP-specific filter syntax (--filter-trait)
   • Added opencode.json configuration file

5. Testing Infrastructure Enhancement

   • Modified LambdaApplicationFactory to ensure minimum 30-second shutdown timeout for test reliability
   • This prevents premature test termination during cleanup

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✅ Checklist

• My changes build cleanly
• I've added/updated relevant tests (N/A - infrastructure changes)
• I've added/updated documentation or README
• I've followed the coding style for this project
• I've tested the changes locally

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🧪 Related Issues or PRs

Modernizes testing infrastructure and improves coverage reporting capabilities.

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💬 Notes for Reviewers

• Primary change: Migration from legacy xUnit runner to Microsoft Testing Platform (MTP)
• MTP provides better integration with modern .NET tooling and native coverage collection
• All test projects have been updated consistently to use the new MTP execution model
• The 30-second minimum shutdown timeout in LambdaApplicationFactory prevents race conditions during test cleanup
• CI workflows now use native .NET coverage instead of requiring external collectors
• Documentation includes comprehensive examples for MTP-specific test filtering syntax

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #288      +/-   ##
==========================================
+ Coverage   87.49%   87.70%   +0.21%     
==========================================
  Files         131      131              
  Lines        3246     3253       +7     
  Branches      318      352      +34     
==========================================
+ Hits         2840     2853      +13     
+ Misses        302      298       -4     
+ Partials      104      102       -2     

Files with missing lines	Coverage Δ
.../MinimalLambda.Testing/LambdaApplicationFactory.cs	69.30% <100.00%> (+1.03%)	⬆️

... and 7 files with indirect coverage changes

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