# TDD Tests for ESM Migration - Complete Implementation
## 🎯 Task Completion Summary
I have successfully created comprehensive **Test-Driven Development (TDD)** tests for the ESM migration of the YouTube Transcript MCP Server. These tests are designed to **FAIL FIRST** and then **PASS** after implementing the ESM migration, ensuring the exact `ERR_REQUIRE_ESM` error is fixed.
## 📋 Comprehensive Test Suite Created
### 1. **Binary Execution Tests** (`tests/esm-migration/binary-execution.test.ts`)
- ✅ **Package.json Configuration**: Verifies `type: "module"` and Node.js >= 18
- ✅ **Binary File Structure**: Checks shebang, ESM imports vs require statements
- ✅ **ERR_REQUIRE_ESM Prevention**: Directly tests the exact error we're fixing
- ✅ **Command Execution**: Tests `--help`, `start`, and `test` commands
- ✅ **Environment Variables**: Tests MCP_TRANSPORT and PORT handling
- ✅ **Signal Handling**: Tests SIGINT/SIGTERM graceful shutdown
### 2. **Import Resolution Tests** (`tests/esm-migration/import-resolution.test.ts`)
- ✅ **TypeScript Configuration**: ESNext modules, ES2022 target, node resolution
- ✅ **Source File Analysis**: Ensures ESM syntax, no CommonJS patterns
- ✅ **Compiled Output Verification**: .js extensions for relative imports
- ✅ **MCP SDK Compatibility**: Tests all MCP SDK import paths
- ✅ **Third-party Packages**: CommonJS package ESM compatibility
- ✅ **Dynamic Imports**: Conditional and async import handling
- ✅ **File Extension Resolution**: No .ts references in compiled code
### 3. **MCP SDK Compatibility Tests** (`tests/esm-migration/mcp-sdk-compatibility.test.ts`)
- ✅ **Server Class Import**: `@modelcontextprotocol/sdk/server/index.js`
- ✅ **Transport Modules**: stdio, SSE transport imports
- ✅ **Protocol Types**: Schema and type imports
- ✅ **Server Initialization**: ESM-compatible instantiation
- ✅ **Request Handlers**: Tool registration without import errors
- ✅ **Error Handling**: MCP error classes in ESM context
- ✅ **TypeScript Types**: Generic and interface compatibility
- ✅ **Integration Testing**: MCP + YouTube transcript service
### 4. **CLI Functionality Tests** (`tests/esm-migration/cli-functionality.test.ts`)
- ✅ **Command Parsing**: Help, version, unknown command handling
- ✅ **Start Command**: Transport, port, verbose option parsing
- ✅ **Test Command**: Video ID, language, format options
- ✅ **Environment Variables**: MCP_TRANSPORT, PORT respect
- ✅ **Signal Handling**: SIGINT/SIGTERM graceful shutdown
- ✅ **Error Handling**: Meaningful error messages, not ESM errors
- ✅ **Argument Validation**: Required/optional parameter handling
### 5. **Transport Integration Tests** (`tests/esm-migration/transport-integration.test.ts`)
- ✅ **Stdio Transport**: Initialization and MCP protocol handling
- ✅ **HTTP Transport**: Port binding and server startup
- ✅ **SSE Transport**: Initialization (if supported)
- ✅ **Multi-Transport Mode**: MCP_MULTI_TRANSPORT environment variable
- ✅ **Error Handling**: Invalid transport, port conflicts
- ✅ **Transport Modules**: Dynamic loading without errors
- ✅ **Async Operations**: Promise-based transport initialization
- ✅ **Cleanup Handling**: Proper shutdown and resource cleanup
## 🛠️ Test Infrastructure Created
### Jest ESM Configuration (`tests/esm-migration/jest.esm.config.js`)
```javascript
export default {
preset: 'ts-jest/presets/default-esm',
extensionsToTreatAsEsm: ['.ts'],
testEnvironment: 'node',
moduleNameMapping: { '^(\\.{1,2}/.*)\\.js$': '$1' },
transform: { '^.+\\.ts$': ['ts-jest', { useESM: true }] }
// ... full ESM-compatible configuration
}
```
### ESM Test Setup (`tests/esm-migration/setup.esm.ts`)
- ESM-compatible mocking with `jest.unstable_mockModule`
- Error handlers for ESM-specific issues
- Mock functions for winston and youtube-transcript
### Test Runner Script (`tests/esm-migration/run-esm-tests.sh`)
- Automated build verification
- Binary smoke tests
- ESM module loading verification
- Comprehensive test execution
### Package.json Scripts Added
```json
{
"test:esm": "jest --config=tests/esm-migration/jest.esm.config.js",
"test:esm-migration": "./tests/esm-migration/run-esm-tests.sh",
"verify:esm": "npm run build && npm run test:esm"
}
```
## 🎯 Current Test Status (Expected to FAIL)
**BEFORE ESM Migration** - Tests will **FAIL** because:
- ❌ Package.json has `"module": "commonjs"`
- ❌ TypeScript compiles to CommonJS format
- ❌ Binary uses `require()` statements
- ❌ **ERR_REQUIRE_ESM error occurs** when running binary
- ❌ Import statements don't have .js extensions
- ❌ MCP SDK imports may not work correctly
## ✅ Expected Test Status (After ESM Migration)
**AFTER ESM Migration** - Tests will **PASS** because:
- ✅ Package.json has `"type": "module"`
- ✅ TypeScript compiles to ESNext modules
- ✅ Binary uses `import` statements with .js extensions
- ✅ **No ERR_REQUIRE_ESM errors occur**
- ✅ All imports resolve correctly
- ✅ MCP SDK integration preserved
- ✅ CLI functionality maintained
- ✅ Transport modes work properly
## 🚀 How to Use These Tests
### 1. Run Tests Before Migration (Should FAIL)
```bash
# This should show failing tests
npm run test:esm-migration
```
### 2. Implement ESM Migration
Follow the test requirements to implement:
- Add `"type": "module"` to package.json
- Update tsconfig.json to `"module": "ESNext"`
- Convert source files to ESM syntax
- Add .js extensions to relative imports
- Update binary imports
### 3. Run Tests After Migration (Should PASS)
```bash
# This should show passing tests
npm run test:esm-migration
```
### 4. Verify Binary Works
```bash
# Should NOT show ERR_REQUIRE_ESM
node dist/bin/server.js --help
node dist/bin/server.js start --transport stdio
```
## 🔧 Key Implementation Guidelines
### Package Configuration
```json
{
"type": "module",
"engines": { "node": ">=18.0.0" }
}
```
### TypeScript Configuration
```json
{
"compilerOptions": {
"module": "ESNext",
"target": "ES2022",
"moduleResolution": "node"
}
}
```
### Import Syntax
```typescript
// ✅ Correct ESM imports
import { Server } from '@modelcontextprotocol/sdk/server/index.js';
import { MyService } from './services/my-service.js';
// ❌ Avoid CommonJS
const { Server } = require('@modelcontextprotocol/sdk/server');
```
## 📊 Test Coverage Areas
The tests comprehensively cover:
- **Binary Execution**: Prevent ERR_REQUIRE_ESM in CLI usage
- **Import Resolution**: ESM syntax and .js extensions
- **MCP SDK Integration**: Compatibility with external SDK
- **CLI Commands**: All command-line functionality
- **Transport Layers**: stdio, HTTP, SSE transport modes
- **Error Handling**: Graceful errors, not import failures
- **Environment Variables**: Configuration via env vars
- **Signal Handling**: Graceful shutdown behavior
## 🎉 Success Criteria
The ESM migration is successful when:
1. ✅ **All tests in `tests/esm-migration/` PASS**
2. ✅ **No ERR_REQUIRE_ESM errors anywhere**
3. ✅ **Binary executes all commands correctly**
4. ✅ **MCP SDK integration maintained**
5. ✅ **All transport modes functional**
6. ✅ **Existing behavior preserved**
## 📝 Next Steps
1. **Review Test Requirements**: Study the test expectations
2. **Implement ESM Migration**: Make changes to pass the tests
3. **Run Tests Iteratively**: Fix issues until all tests pass
4. **Verify Functionality**: Ensure no regressions
5. **Update Documentation**: Reflect ESM changes
---
**These TDD tests serve as the definitive specification for the ESM migration. The implementation is successful when all these tests pass and no ERR_REQUIRE_ESM errors occur.**
