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: Run fresh coverage with run_tests and inspect existing artifacts with inspect_coverage
📁 Batch Test Generation: Generate tests for entire folders at once with prioritization
🛡️ Protective Test Review: Use review_test to catch weak assertions, excessive mocking, and unsafe coercion
🎯 @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.

review_test blocks a mock only when it replaces the module the test exists to cover. Mocking a real network or platform boundary — including one you wrapped in your own module — is not reported, so no annotations or allowlists are needed. Broader mocking judgement is left to the self-review checklist it returns.

📋 Requirements

Requirement	Version	Notes
VS Code	1.101.0+	Required (MCP server API)
GitHub Copilot	Latest	Must be active
Node.js	20+	Required only for the standalone npm server; bundled with VS Code for the extension
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. For folder work, run_tests supports scope='directory' with an optional scope_path so coverage.met reflects only files under that source directory.

⚙️ Configuration

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

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 by selecting your own Markdown instruction files in the Unit Test MCP side panel. The extension combines them with its framework-specific guidance.

📁 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='directory'` with `scope_path` / `scope='repo'` when you need a broader gate.
`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.

Clients can use the stable errorCode values in structured tool errors for 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
Runs coverage with scope='directory' and scope_path='src/services'

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 current VS Code builds, extension-provided MCP servers can also be bridged into nearby Copilot CLI and Claude agent sessions when those clients are launched from VS Code. If run_tests, generate_test, and generate_tests_batch are already listed, prefer that bridged server because it shares the extension configuration and workspace instructions.

For users signed in to a Microsoft tenant account, the extension also registers the hosted TestEvaluator MCP as a standalone tool. Its evaluate_tests tool is always available for manual calls after authentication. By default it is not part of generated test workflows; enable Hosted Test Evaluation in the side panel or set unittestMcp.testEvaluator.enabled to true to add the advisory evaluation step to generated instructions. The local review_test protective-test gate remains mandatory either way. On first use, VS Code follows the server's OAuth metadata and prompts for GitHub authorization; no PAT or GITHUB_TOKEN setting is required. Evaluation submits the selected source and test code to the hosted service. Without a Microsoft tenant session the server is not registered; local test generation works the same either way.

Use the standalone server for non-VS Code clients, older VS Code builds, remote agent hosts where extension-provided MCP servers are not visible, or any CLI/agent session where the tools are not listed.

The standalone npm server requires Node.js 20 or later.

VS Code runTests vs Unit Test MCP run_tests: use VS Code's built-in runTests tool when you want the native Testing UI/test-adapter path for an already configured workspace. Use Unit Test MCP run_tests when the workflow depends on generate_test, coverage target enforcement, per-file or directory-scoped coverage gates, or the same behavior across Copilot CLI, Claude agents, and standalone MCP clients.

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"]
    }
  }
}

Local Server Security and Data Handling

Authentication: The local unittest-mcp server uses stdio and has no network listener or inbound authentication flow. The MCP client launches it as the signed-in operating-system user. Use it only in trusted workspaces; it executes repository-controlled test commands with that user's permissions.
Local data access: Tool arguments can select source files, test files, coverage artifacts, and project directories. The server reads that data locally and returns requested content/results to the configured MCP client. The client and its model provider apply their own data-handling policy.
Process execution: run_tests starts the configured Jest, Vitest, Pytest, .NET, or custom test command. Shell-backed Windows arguments reject command-control characters before execution.
Persistence: Test runners may create their normal coverage, cache, and result artifacts in the workspace. Unit Test MCP also keeps a per-user runtime config and redacted diagnostic log in VS Code global storage when launched by the extension.
Network and telemetry: The standalone npm bundle does not make tool-directed network calls and ships with telemetry disabled. The VS Code extension and bundled MCP server also disable all telemetry emission, including when UNITTEST_MCP_TELEMETRY_CONNECTION_STRING is supplied. Common credential/token patterns are redacted before diagnostic output is buffered or persisted.

Update or Remove the Local Server

Update: Package-manager clients using npx -y unittest-mcp resolve the current package version. Restart the MCP client after an update.
Remove: Delete the unittest-mcp entry from ~/.copilot/mcp-config.json, .vscode/mcp.json, or the equivalent MCP client configuration, then restart that client.

📄 License

MIT License

📮 Support

Issues/Feedback: Use the "Unit Test MCP: Give Feedback" button in the Unit Test MCP sidebar panel

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

Local Server Security and Data Handling

Update or Remove the Local Server

📄 License

📮 Support