[WIP] Implement DELETE User Functionality

[Copilot]

Implementation Plan: DELETE User Functionality

This PR implements the missing DeleteUser endpoint following TDD principles and project conventions.

Changes Required:

• Create test project at solution level (net-users-api.tests/)
• Add xUnit test infrastructure with proper dependencies
• Write unit tests for DeleteUser functionality (TDD - Red phase)
  • Test successful deletion (204 No Content)
  • Test user not found (404 Not Found)
  • Test logging behavior
• Implement DeleteUser method in UsersController (Green phase)
  • Remove user from _users list
  • Return NoContent (204) on success
  • Return NotFound (404) with error message if user doesn't exist
  • Add proper logging
• Verify all tests pass (Green phase complete)
• Run security checks - Fixed log forging vulnerability
• Manual testing completed successfully
• Address code review feedback - Made logging consistent
• Add TDD rationale documentation
• Ready for final review

Approach:

Following Test-Driven Development (TDD):

1. ✅ Write failing tests first (Red)
2. ✅ Implement minimal code to make tests pass (Green)
3. ✅ Refactor - Fixed security issue and improved consistency

TDD Rationale (Added to Code):

A comprehensive comment has been added to the DeleteUser method explaining the 6 key reasons TDD was chosen:

1. Requirements clarity through test-first design
2. Regression prevention with comprehensive coverage
3. Better design quality through test-driven decisions
4. Tests as executable documentation
5. High confidence in correctness (9/9 tests passing)
6. Alignment with project's educational goals

Test Results:

• 9 tests total: 9 passed ✅
  • 6 tests for existing functionality (GetUsers, GetUser, CreateUser, UpdateUser)
  • 3 tests for new DeleteUser functionality

Manual Testing:

✅ DELETE /api/v1/users/2 → 204 No Content (user deleted)
✅ GET /api/v1/users → User 2 no longer in list
✅ DELETE /api/v1/users/nonexistent → 404 Not Found with error message
✅ DELETE /api/v1/users/2 (again) → 404 Not Found (already deleted)
✅ Logging verified - consistent with existing patterns

Security:

✅ CodeQL scan passed - 0 vulnerabilities
✅ No log forging vulnerabilities
✅ No vulnerabilities in dependencies (Moq 4.20.72, Microsoft.AspNetCore.Mvc.Testing 9.0.9)

Code Quality:

✅ Follows existing code patterns and conventions
✅ Logging pattern consistent with other controller methods
✅ Uses ILogger dependency injection
✅ Returns appropriate HTTP status codes
✅ Includes XML documentation
✅ Comprehensive test coverage with proper test isolation
✅ TDD rationale documented in code

Files Modified:

• net-users-api/Controllers/UsersController.cs - Implemented DeleteUser method with TDD rationale comment
• net-users-api/net-users-api.csproj - Added InternalsVisibleTo for test access
• net-users-api.tests/ - New test project with comprehensive tests
  • Added xUnit, Moq, and Microsoft.AspNetCore.Mvc.Testing packages
  • Created UsersControllerTests.cs with full coverage and proper test isolation

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement DELETE User Functionality</issue_title>
<issue_description>## Description
Implement the missing DeleteUser endpoint in the UsersController. Currently, the DELETE endpoint exists but throws NotImplementedException.

Requirements

• Implement DeleteUser(string id) method in UsersController
• Delete user from the in-memory _users list
• Return NoContent (204) on successful deletion
• Return NotFound (404) if user doesn't exist with appropriate error message
• Add logging for the delete operation
• Follow existing code patterns and conventions

Acceptance Criteria

• ✅ DELETE endpoint properly removes users from the list
• ✅ Returns 204 No Content on successful deletion
• ✅ Returns 404 Not Found for non-existent users
• ✅ Logs the delete operation
• ✅ Comprehensive unit tests added to UsersControllerTests.cs
• ✅ All new and existing tests pass

Additional Notes

• Follow the same patterns used in other controller methods
• Ensure tests cover both success and failure scenarios
• Mock ILogger appropriately in tests</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #7

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