Test Generator Skill

🎯 Use Case Demo

Scenario

Developer Mike just wrote a new BookingService with 5 methods. He needs unit tests but testing takes forever to write.

Before (Manual):

csharp

// Spend 30 minutes writing one test...
[Fact]
public void CreateBooking_ValidData_ReturnsBooking()
{
    // Arrange... Act... Assert... 😴
}

After (With Skill):

"Generate tests for BookingService.cs"

csharp

public class BookingServiceTests
{
    private readonly Mock<IFlightRepository> _flightRepo;
    private readonly Mock<IBookingRepository> _bookingRepo;
    private readonly BookingService _sut;

    public BookingServiceTests()
    {
        _flightRepo = new Mock<IFlightRepository>();
        _bookingRepo = new Mock<IBookingRepository>();
        _sut = new BookingService(_flightRepo.Object, _bookingRepo.Object);
    }

    [Fact]
    public void CreateBooking_WithValidFlight_ReturnsNewBooking()
    {
        // Arrange
        var flight = new Flight { Id = 1, AvailableSeats = 10 };
        _flightRepo.Setup(r => r.GetById(1)).Returns(flight);
        
        // Act
        var result = _sut.CreateBooking(1, "John Doe", "john@example.com");
        
        // Assert
        Assert.NotNull(result);
        Assert.Equal("John Doe", result.PassengerName);
    }

    [Fact]
    public void CreateBooking_FlightNotFound_ThrowsException()
    {
        // Arrange
        _flightRepo.Setup(r => r.GetById(99)).Returns((Flight)null);
        
        // Act & Assert
        Assert.Throws<FlightNotFoundException>(() => 
            _sut.CreateBooking(99, "John", "john@example.com"));
    }

    [Theory]
    [InlineData("")]
    [InlineData(null)]
    [InlineData("   ")]
    public void CreateBooking_InvalidPassengerName_ThrowsValidationException(string name)
    {
        // Arrange & Act & Assert
        Assert.Throws<ValidationException>(() => 
            _sut.CreateBooking(1, name, "john@example.com"));
    }

    // ... 10 more comprehensive tests generated
}

Time Saved: 2-3 hours per service class

When to Use This Skill

•After writing new code
•When improving test coverage
•Before submitting PRs
•For TDD (write tests first)

Test Types Generated

Type	Purpose	Example
Happy Path	Normal operation	Valid input → expected output
Edge Cases	Boundary conditions	Empty, null, max values
Error Cases	Exception handling	Invalid input → proper exception
Integration	Component interaction	Service → Repository → DB

Agent Instructions

When user asks for tests:

•
Read the source file to understand:
- •Class structure and dependencies
- •Public methods to test
- •Input/output types
- •Possible exceptions
•
Identify test scenarios:
- •Happy path for each method
- •Null/empty inputs
- •Boundary values
- •Exception conditions
•
Generate test class:
- •Setup with mocks
- •Arrange-Act-Assert pattern
- •Descriptive test names
- •Theory/InlineData for parameterized tests
•
Match project framework:
- •.NET → xUnit + Moq
- •Node.js → Jest
- •Python → pytest

Example Prompts

User: "Write tests for BookingService" → Generate comprehensive test file

User: "Add edge case tests for CreateBooking method" → Focus on specific method edge cases

User: "What scenarios should I test?" → List test cases without code

Demo Script

bash

# 1. Show existing service
cat Services/BookingService.cs

# 2. Ask agent: "Generate unit tests for BookingService"

# 3. Agent creates BookingServiceTests.cs with:
#    - 15+ test methods
#    - Mocked dependencies
#    - Edge cases covered

# 4. Run tests
dotnet test

Benefits

Metric	Before	After	Improvement
Test writing time	2-3 hours	5 minutes	⬇️ 95%
Test coverage	30-50%	80-90%	⬆️ 2x
Edge cases found	Often missed	Comprehensive	✅ Complete
TDD adoption	Difficult	Easy	✅ Enabled