Generating Unit Tests with GitHub Copilot Agent Mode

One of the most powerful applications of GitHub Copilot's Agent mode is its ability to help you generate comprehensive unit tests. Let's explore how to make the most of this feature.

Why Use Agent Mode for Testing?

Agent mode is particularly well-suited for test generation because it:

• Has access to your entire workspace
• Can analyze multiple files simultaneously
• Understands project context and dependencies
• Can generate tests across different testing frameworks
• Maintains consistency with existing test patterns

Getting Started

1. Setting Up Your Request

When asking Copilot to generate tests, provide:

• The target file or component to test
• Your preferred testing framework
• Any specific testing patterns or conventions
• Coverage requirements
• Special testing considerations

Example prompt:

"Generate unit tests for UserService.cs using xUnit. Include tests for all public methods and follow our existing pattern of Arrange-Act-Assert."

2. Best Practices for Test Generation

Structure Your Request

• Start with the scope ("Generate unit tests for...")
• Specify the framework ("using xUnit/Jest/NUnit...")
• Mention any patterns ("following AAA pattern...")
• Include special cases ("ensure edge cases are covered...")

Example Prompts

Basic request:

"Create unit tests for the OrderProcessor class in the Services folder"

Detailed request:

"Generate unit tests for the PaymentService class with mocked dependencies. Include happy path and error scenarios, and ensure we're testing all payment methods."

Advanced Techniques

1. Generating Test Suites

Agent mode can create entire test suites. Example prompt:

"Create a complete test suite for our authentication system, including tests for login, registration, password reset, and token validation"

2. Testing Edge Cases

Help Copilot identify edge cases:

"Generate tests for the FileProcessor class, including cases for:
- Empty files
- Large files
- Invalid file formats
- Permission issues
- Concurrent access"

3. Mock Generation

Agent mode can help with complex mocking:

"Create tests for the EmailService, mocking the SMTP client and template engine. Include verification of sent emails and template rendering"

Pro Tips

1. Iterative Refinement

   • Start with basic test coverage
   • Ask for additional test cases
   • Request specific edge cases
   • Fine-tune assertions

2. Coverage Analysis

   • Ask Copilot to analyze coverage gaps
   • Request tests for uncovered scenarios
   • Verify critical paths

3. Maintenance Workflow

   "Update the OrderProcessor tests to cover the new refund functionality, maintaining our existing test patterns"
   

Common Patterns

1. Data-Driven Tests

"Generate data-driven tests for the ValidateAddress method, covering different address formats and validation rules"

2. Integration Test Setup

"Create integration tests for the ProductController, including database setup and cleanup for each test"

3. Behavior-Driven Development (BDD)

"Generate BDD-style tests for the shopping cart checkout process, covering the full user journey"

Troubleshooting Tips

1. If Tests Are Too Basic

   • Request more specific test cases
   • Ask for edge case coverage
   • Specify validation criteria

2. If Tests Are Missing Context

   • Provide more project background
   • Reference existing test patterns
   • Specify dependencies and mocking requirements

3. If Tests Need Refinement

   • Request specific improvements
   • Ask for additional assertions
   • Specify error scenarios

Best Practices Checklist

✅ Start with clear test objectives
✅ Specify testing framework and patterns
✅ Include both positive and negative test cases
✅ Request mock generation for dependencies
✅ Verify edge cases and error handling
✅ Maintain consistency with existing tests
✅ Include cleanup and tear-down logic
✅ Document test assumptions and requirements

Example Workflow

1. Initial Setup

   "Set up a test project for our API controllers using xUnit and Moq"
   

2. Basic Coverage

   "Generate tests for the basic CRUD operations in UserController"
   

3. Edge Cases

   "Add tests for validation errors and edge cases in the UserController"
   

4. Integration

   "Create integration tests for the user registration flow"
   

Conclusion

GitHub Copilot's Agent mode is a powerful ally in test generation, capable of understanding your project context and creating comprehensive test suites. By following these patterns and practices, you can efficiently generate high-quality tests that improve your code's reliability and maintainability.

Remember: While Copilot can generate excellent test templates and coverage, always review and adjust the generated tests to ensure they meet your specific requirements and edge cases. Use it as a collaborative tool to enhance your testing process, not as a complete replacement for thoughtful test design.