Copilot Unit Test Generator Extension (Training Version)

A simple VS Code extension that generates unit tests using GitHub Copilot's Language Model API. Perfect for learning how to build VS Code extensions with AI capabilities.

Features

• 🤖 AI-Powered Test Generation: Uses GitHub Copilot's GPT-4 model to generate comprehensive unit tests
• 🌐 25+ Languages Supported: JavaScript, TypeScript, Python, Java, C#, Go, Ruby, PHP, Rust, C/C++, Swift, Kotlin, Scala, R, Dart, Elixir, Haskell, Julia, Perl, Groovy, Lua, Clojure, and more!
• 🧪 Framework Auto-Detection: Automatically selects the right test framework (Jest, pytest, JUnit, xUnit, RSpec, PHPUnit, etc.)
• 🎯 Context Menu Integration: Right-click on selected code to generate tests
• 📂 Smart File Creation: Automatically creates test files with language-specific naming conventions
• ⚡ Simple & Focused: Minimal implementation perfect for learning

Prerequisites

Before you begin, ensure you have:

1. Node.js (v18 or higher) - Download here
2. Visual Studio Code (v1.85.0 or higher)
3. GitHub Copilot subscription and extension installed
4. npm or yarn package manager

Installation & Setup

Step 1: Install Dependencies

Open a terminal in the extension directory and run:

npm install

This installs the required VS Code API types.

Step 2: Install VSCE (VS Code Extension Manager)

npm install -g @vscode/vsce

Testing the Extension Locally

Method 1: Press F5 (Recommended for Development)

1. Open the extension folder in VS Code
2. Press F5 or go to Run > Start Debugging
3. A new VS Code window will open with your extension loaded
4. Open any code file and select some code
5. Right-click and choose "Generate Unit Tests with Copilot"

Method 2: Using Command Palette

1. In the Extension Development Host window
2. Press Ctrl+Shift+P (or Cmd+Shift+P on Mac)
3. Type: Generate Unit Tests with Copilot
4. Press Enter

Test with Sample Code

Create a test file sample.js:

function add(a, b) {
    return a + b;
}

function multiply(a, b) {
    return a * b;
}

function divide(a, b) {
    if (b === 0) {
        throw new Error('Cannot divide by zero');
    }
    return a / b;
}

module.exports = { add, multiply, divide };

1. Select the functions
2. Right-click → Generate Unit Tests with Copilot
3. Test file sample.test.js will be created automatically

Packaging the Extension

Create a .vsix Package

vsce package

This creates a .vsix file (e.g., copilot-test-generator-simple-0.1.0.vsix)

Install the .vsix Locally

code --install-extension copilot-test-generator-simple-0.1.0.vsix

Or manually:

1. Open VS Code
2. Go to Extensions (Ctrl+Shift+X)
3. Click the "..." menu at the top
4. Choose "Install from VSIX..."
5. Select your .vsix file

Publishing to VS Code Marketplace

Step 1: Create a Publisher Account

1. Go to Visual Studio Marketplace Publisher Management
2. Sign in with your Microsoft account
3. Create a publisher (e.g., "mycompany")

Step 2: Get a Personal Access Token (PAT)

1. Go to Azure DevOps
2. Click on User Settings (top right) → Personal Access Tokens
3. Create new token with:
   • Name: VS Code Extensions
   • Organization: All accessible organizations
   • Scopes: Marketplace → Manage
   • Expiration: 90 days (or custom)
4. Copy the token immediately (you won't see it again!)

Step 3: Login to VSCE

vsce login your-publisher-name

Enter your Personal Access Token when prompted.

Step 4: Update package.json Publisher

In package.json, change:

"publisher": "your-actual-publisher-name"

Step 5: Publish

vsce publish

Or publish with version bump:

vsce publish minor  # 0.1.0 → 0.2.0
vsce publish patch  # 0.1.0 → 0.1.1
vsce publish major  # 0.1.0 → 1.0.0

Step 6: Verify Publication

Visit: https://marketplace.visualstudio.com/items?itemName=your-publisher-name.copilot-test-generator-simple

Supported Languages & Frameworks

How It Works

Architecture Overview

User selects code
    ↓
Right-click menu
    ↓
Extension activates
    ↓
Detects language & framework
    ↓
Calls Copilot Language Model API (vscode.lm)
    ↓
Generates test code with proper imports
    ↓
Creates test file (language-specific naming)
    ↓
Opens in editor

Key Code Components

1. Command Registration (extension.js):

   • Registers copilot-test-generator.generateTests command
   • Adds context menu item for selected code

2. Copilot API Integration:

   • Uses vscode.lm.selectChatModels() to access Copilot
   • Sends structured prompts for test generation
   • Handles streaming responses

3. Test File Creation:

   • Determines test file naming based on language
   • Creates files in the same directory as source
   • Auto-opens generated tests

Customization Ideas

Want to enhance this extension? Try:

1. Add Configuration Settings:

   • Test framework selection
   • Custom test file location
   • Coverage requirements

2. Support More Languages:

   • Add language detection
   • Framework-specific templates

3. Enhance Prompts:

   • Include project context
   • Add specific test patterns
   • Request specific coverage

4. Add Commands:

   • Generate tests for entire file
   • Update existing tests
   • Generate mocks

Troubleshooting

"No Copilot model available"

• Ensure GitHub Copilot extension is installed and active
• Check your Copilot subscription is valid
• Sign in to GitHub in VS Code

Extension doesn't activate

• Check VS Code version (must be 1.85.0+)
• Verify activationEvents in package.json
• Check Output panel (Help → Toggle Developer Tools → Console)

Tests not generating

• Check VS Code Output panel for errors
• Ensure you have code selected
• Verify language is supported

VSCE publish fails

• Check publisher name matches your account
• Verify PAT token has Marketplace→Manage scope
• Ensure version number increased

Learning Resources

• VS Code Extension API
• Language Model API
• Publishing Extensions
• Extension Samples

Project Structure

unit_test_extension/
├── extension.js          # Main extension logic
├── package.json          # Extension manifest
├── README.md            # This file
└── .vscodeignore        # Files to exclude from package

License

MIT - Feel free to use this for learning and training purposes!

Next Steps

1. ✅ Test the extension locally (F5)
2. ✅ Try with different programming languages
3. ✅ Package the extension (.vsix)
4. ✅ Publish to marketplace (optional)
5. 🚀 Enhance with your own features!

Happy Coding! 🎉

Built with ❤️ using GitHub Copilot's Language Model API