Add comprehensive README for test project

Co-authored-by: omegaleo <5655201+omegaleo@users.noreply.github.com>

OmegaLeo.HelperLib.Tests/README.md

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+# OmegaLeo.HelperLib.Tests
+
+Comprehensive test suite for the OmegaLeo.HelperLib library.
+
+## Overview
+
+This project contains xUnit tests that validate the functionality of the HelperLib library. The tests run automatically in CI/CD pipelines to catch errors before they reach production.
+
+## Test Coverage
+
+### Extension Methods
+
+#### MathExtensions (8 tests)
+- `AverageWithNullValidation` for int, double, and float types
+- Empty list handling
+- Single value handling  
+- Negative value handling
+
+#### IListExtensions (14 tests)
+- `Swap` - by indices and by items
+- `Replace` - existing and non-existing items
+- `Random` - single element and multiple elements
+- `Shuffle` - list randomization
+- Edge cases (empty lists, invalid parameters)
+
+### Helper Utilities
+
+#### BenchmarkUtility (8 tests)
+- `Record` - execution time measurement
+- `RecordAndSaveToResults` - saved benchmarks
+- `Start` / `Stop` - manual timing
+- `ClearResults` - cleanup functionality
+- `GetResults` / `GetAllResults` - result retrieval
+
+### Models
+
+#### NeoDictionary (12 tests)
+- `Add` and `TryGetValue` operations
+- `TryGetValueFromIndex` - indexed access
+- `ToDictionary` - conversion to standard Dictionary
+- LINQ operations (`Any`, `Where`, `FirstOrDefault`, `LastOrDefault`)
+- `AddRange` - bulk operations
+- `Count` - size queries
+
+## Running Tests
+
+### Run all tests
+```bash
+dotnet test
+```
+
+### Run tests for a specific project
+```bash
+dotnet test OmegaLeo.HelperLib.Tests/OmegaLeo.HelperLib.Tests.csproj
+```
+
+### Run tests with detailed output
+```bash
+dotnet test --verbosity normal
+```
+
+### Run tests with code coverage
+```bash
+dotnet test --collect:"XPlat Code Coverage"
+```
+
+## Test Structure
+
+Tests are organized by the area of code they test:
+
+```
+OmegaLeo.HelperLib.Tests/
+├── Extensions/
+│   ├── MathExtensionsTests.cs
+│   └── IListExtensionsTests.cs
+├── Helpers/
+│   └── BenchmarkUtilityTests.cs
+└── Models/
+    └── NeoDictionaryTests.cs
+```
+
+## Writing New Tests
+
+When adding new functionality to the library, follow these guidelines:
+
+1. **Create tests first** (TDD approach recommended)
+2. **Use descriptive test names** following the pattern: `MethodName_Scenario_ExpectedResult`
+3. **Follow the AAA pattern**:
+   - **Arrange**: Set up test data
+   - **Act**: Execute the method being tested
+   - **Assert**: Verify the results
+4. **Test edge cases**: empty collections, null values, boundary conditions
+5. **Test error conditions**: ensure exceptions are thrown when expected
+
+### Example Test Structure
+
+```csharp
+[Fact]
+public void MethodName_Scenario_ExpectedResult()
+{
+    // Arrange
+    var input = new List<int> { 1, 2, 3 };
+    
+    // Act
+    var result = input.MyExtensionMethod();
+    
+    // Assert
+    Assert.Equal(expectedValue, result);
+}
+```
+
+## Continuous Integration
+
+Tests run automatically on:
+- **Pull Requests** to the main branch
+- **Pushes** to the main branch
+
+The CI workflow (`.github/workflows/dotnet.yml`) is configured to:
+1. Restore dependencies
+2. Build the solution
+3. Run all tests
+4. Report results
+
+Pull requests must pass all tests before they can be merged.
+
+## Test Frameworks and Tools
+
+- **xUnit** - Testing framework
+- **coverlet.collector** - Code coverage collection
+- **Microsoft.NET.Test.Sdk** - Test SDK
+
+## Current Test Status
+
+✅ **42 tests passing**
+- MathExtensions: 8 tests
+- IListExtensions: 14 tests  
+- BenchmarkUtility: 8 tests
+- NeoDictionary: 12 tests
+
+## Contributing
+
+When contributing to this project:
+
+1. Ensure all existing tests pass
+2. Add tests for any new functionality
+3. Maintain at least the current level of code coverage
+4. Follow the existing test naming and structure conventions
+
+## Troubleshooting
+
+### Tests fail locally but pass in CI
+- Ensure you're using .NET 8.0 SDK
+- Run `dotnet restore` to update dependencies
+- Clear bin/obj folders and rebuild
+
+### Tests pass locally but fail in CI
+- Check for environment-specific assumptions
+- Ensure tests are deterministic (not dependent on timing, randomness, etc.)
+- Review test output logs in the CI workflow
+
+## Related Documentation
+
+- [Main Library README](../README.md)
+- [Contributing Guidelines](../CONTRIBUTING.md)
+- [CI Workflow](.github/workflows/dotnet.yml)