Unit Test MCP

Intelligent test generation and execution for GitHub Copilot

A VS Code extension that enables GitHub Copilot to generate, run, and improve Jest, Vitest, Pytest, and .NET tests using the Model Context Protocol (MCP).

✨ Features

🚀 Zero Setup: Install and use immediately — MCP server registers automatically via the VS Code API
🧪 Multi-Framework Support: Jest/Vitest (JS/TS), Pytest (Python), and .NET (C#)
🤖 AI-Powered: Works seamlessly with GitHub Copilot Chat
📊 Coverage Reports: Get instant test coverage feedback with inspect_coverage
📁 Batch Test Generation: Generate tests for entire folders at once with prioritization
🎯 @UnitTestEngineer Agent: Built-in custom agent for test generation, coverage improvement, and batch workflows
📝 Copilot Instructions: Auto-creates and syncs workspace instruction files that teach Copilot the test workflow
📖 Getting Started Walkthrough: Built-in tutorial accessible via Unit Test MCP: Open Tutorial

📦 Installation

Install from the VS Code Marketplace or search for "Unit Test MCP" in the Extensions view (Ctrl+Shift+X).

🚀 Quick Start

1. Install the Extension

Install from the Marketplace link above. The extension auto-configures on first activation.

2. Start Using with Copilot

Open GitHub Copilot Chat and try:

Generate unit tests for this file

Generate tests for all files in src/

Run tests with coverage

What files have low coverage?

Or use the built-in @UnitTestEngineer agent for a guided workflow.

The extension will automatically activate and handle the requests.

📋 Requirements

Requirement	Version	Notes
VS Code	1.101.0+	Required (MCP server API)
GitHub Copilot	Latest	Must be active
Node.js	N/A	Bundled with VS Code
Python	Any	Only needed if running Pytest tests
.NET SDK	6.0+	Only needed if running .NET tests

🎯 What You Can Do

With Jest or Vitest (JavaScript/TypeScript)

✅ Generate JS/TS unit tests (including React component tests)
✅ Run tests with coverage
✅ Watch mode support
✅ Targeted test execution
✅ Update snapshots (Jest, via --updateSnapshot, when applicable)

With Pytest (Python)

✅ Generate Python unit tests
✅ Run tests with coverage
✅ Parametrized test support
✅ Fixture-based testing

With .NET (C#)

✅ Generate xUnit/NUnit tests
✅ Run tests via dotnet test
✅ Coverage reporting
✅ Solution-aware test generation

Coverage Reports

Ask Copilot "Run tests with coverage" or "What files have low coverage?" to get an interactive coverage report showing per-file line, branch, function, and statement coverage.

Coverage Report

⚙️ Configuration

The extension works out-of-the-box, but you can customize it using the Unit Test MCP side panel.

Side Panel UI

Open the Unit Test MCP view in the VS Code sidebar (look for the clipboard/gear icon in the Activity Bar).
Use the UI to:
- Browse and select custom instruction files for Jest, Vitest, Pytest, or .NET.
- View currently loaded instructions.
- Set target code coverage percentage.
- Configure custom test commands.

Changes take effect immediately - no restart required!

📝 Custom Instructions

Customize test generation with your own instructions! See CUSTOM_INSTRUCTIONS.md for details.

📁 Generated Files & Git

The extension creates files in your workspace that Copilot reads at runtime:

.github/instructions/unittestMcp.instructions.md   # Auto-synced on each activation
.github/prompts/UnitTestMcp.UnitTestEngineer.agent.md  # Created once, never overwritten

These files work whether committed or gitignored — Copilot reads them from the filesystem. To keep your git history clean, add this to your .gitignore:

# Unit Test MCP (auto-managed by extension)
**/.github/instructions/unittestMcp.instructions.md
**/.github/prompts/UnitTestMcp.UnitTestEngineer.agent.md

Each developer's copy is managed independently by the extension — no commits needed.

💡 How It Works

┌─────────────────────────┐
│   GitHub Copilot Chat   │
└───────────┬─────────────┘
            │ MCP Protocol
┌───────────▼─────────────┐
│  TypeScript MCP Server  │
│  (Bundled in Extension) │
└───────────┬─────────────┘
            │
┌───────────▼─────────────┐
│ Jest / Vitest / Pytest  │
│        / Dotnet         │
└─────────────────────────┘

You ask Copilot to generate/run tests
Copilot calls the MCP server via standard protocol
Server executes Jest/Vitest/Pytest/.NET and returns results
Copilot shows you formatted output

🐛 Troubleshooting

Extension Not Working?

Check Status:

Open the Unit Test MCP sidebar view.
Verify that the server is connected and configuration is valid.

Still not working?

Reload VS Code: Ctrl+Shift+P → "Reload Window"
Check Output panel: View → Output → Select "Log (Extension Host)" and search for "Unit Test MCP"

Copilot Doesn't See the Tools?

Ensure GitHub Copilot extension is installed and active
Run MCP: List Servers from the Command Palette — "Unit Test MCP" should appear
If not listed, reload VS Code: Ctrl+Shift+P → "Reload Window"
Try asking: "What MCP tools are available?"

Tests Not Running?

For Jest:

Ensure package.json exists in your project root
Verify Jest is installed: npm list jest

For Vitest:

Ensure package.json exists in your project root
Verify Vitest is installed: npm list vitest

For Pytest:

Ensure Python is installed: python --version
Verify Pytest is installed: pip list | grep pytest

For .NET:

Ensure .NET SDK is installed: dotnet --version
Ensure your project is a valid .NET project

Structured Error Codes

When a tool call fails, the response carries isError: true with a human-readable message in content[0].text and a machine-readable envelope in structuredContent.error of the form:

{
  "error": {
    "code": "INVALID_ROOT_DIR",
    "message": "root_dir is required and must be a non-empty string",
    "details": { /* optional, code-specific */ }
  }
}

Agents should branch on code rather than parsing message. Common recovery cases include:

Code	What to do
`INVALID_INPUT`	Correct the argument named in `details.issues[].path`.
`INVALID_ROOT_DIR`	Pass an absolute project directory containing files such as `package.json`, `*.csproj`, or `pytest.ini`.
`INVALID_SCOPE`	Add `test_pattern` when using `scope='file'`, or use `scope='auto'` / `'repo'`.
`NO_FRAMEWORK_DETECTED`	Pass an explicit `framework` such as `jest`, `vitest`, `pytest`, `dotnet`, or `custom`.
`TIMEOUT`	Retry with a larger `timeout_ms`, or investigate hanging tests.
`SPAWN_FAILED`	Verify `node`, `python`, or `dotnet` is installed and available on `PATH`.
`INTERNAL`	File an issue with the message and reproduction steps.

The complete enum is exported as MCP_TOOL_ERROR_CODES from src/mcp/errors.ts for clients that need exhaustive handling.

Back-compat: consumers that only read content[0].text continue to work — structuredContent.error is additive.

📚 Examples

Example 1: Generate React Tests

You: Generate unit tests for src/components/Button.tsx

Copilot: [Uses generate_test tool]
Creates: src/components/__tests__/Button.test.tsx

Example 2: Run Tests with Coverage

You: Run tests with coverage for the Button component

Copilot: [Uses run_tests tool]
Shows: Test results + coverage report

Example 3: Batch Test Generation

You: Generate tests for all files in src/services/

Copilot: [Uses generate_tests_batch tool]
Scans folder, prioritizes by missing tests/low coverage
Creates tests for each file sequentially

Example 4: Inspect Coverage

You: What files have low test coverage?

Copilot: [Uses inspect_coverage tool]
Shows: Worst-covered files and branches from existing coverage artifacts

🖥️ Using with Copilot CLI

The VS Code extension automatically registers the MCP server for VS Code's built-in Copilot Chat. In newer VS Code builds, copilot chat terminal sessions may also see extension-provided MCP tools. For non-VS Code clients, background agents, or any CLI session where the tools are not listed, use the standalone server.

To add the standalone server:

Open a Copilot CLI session (type copilot in VS Code's integrated terminal)
Run /mcp add and fill in the form:
- Server Name: unittest-mcp
- Server Type: STDIO (or Local)
- Command: npx -y unittest-mcp
- Environment Variables: {} (leave empty)
- Tools: *
Press Ctrl+S to save — the tools are available immediately

Alternatively, edit ~/.copilot/mcp-config.json directly:

{
  "mcpServers": {
    "unittest-mcp": {
      "type": "local",
      "command": "npx",
      "args": ["-y", "unittest-mcp"],
      "env": {},
      "tools": ["*"]
    }
  }
}

Or add it to your workspace .vscode/mcp.json for VS Code-level access:

{
  "servers": {
    "unittest-mcp": {
      "command": "npx",
      "args": ["-y", "unittest-mcp"]
    }
  }
}

📄 License

MIT License - see LICENSE file for details

📮 Support

Issues/Feedback: Use the "Unit Test MCP: Give Feedback" button in the Unit Test MCP sidebar panel
Repository: GitHub (Internal Microsoft access only)

🏗️ For Developers

See DEVELOPMENT.md for local development setup, building from source, testing, and publishing.

Unit Test MCP

Kenneth Huang

Unit Test MCP

✨ Features

📦 Installation

🚀 Quick Start

1. Install the Extension

2. Start Using with Copilot

📋 Requirements

🎯 What You Can Do

With Jest or Vitest (JavaScript/TypeScript)

With Pytest (Python)

With .NET (C#)

Coverage Reports

⚙️ Configuration

📝 Custom Instructions

📁 Generated Files & Git

💡 How It Works

🐛 Troubleshooting

Extension Not Working?

Copilot Doesn't See the Tools?

Tests Not Running?

Structured Error Codes

📚 Examples

Example 1: Generate React Tests

Example 2: Run Tests with Coverage

Example 3: Batch Test Generation

Example 4: Inspect Coverage

🖥️ Using with Copilot CLI

📄 License

📮 Support

🏗️ For Developers