Add comprehensive tests for non-ESM usage backward compatibility

- Enhanced CommonJS require test with full end-to-end functionality
- Added test for CommonJS bundling with esbuild
- Verified all existing tests still pass
- Ensured no regression for CommonJS users

Co-authored-by: naorpeled <[email protected]>

Author: Copilot

__tests__/esm-bundle.unit.js

@@ -46,10 +46,10 @@ export const handler = async (event, context) => {
 
     fs.writeFileSync(testFilePath, testCode);
 
-    // Bundle with esbuild
+    // Bundle with esbuild (mark AWS SDK as external since they're peer dependencies)
     try {
       execSync(
-        `npx esbuild ${testFilePath} --bundle --platform=node --format=esm --outfile=${bundlePath}`,
+        `npx esbuild ${testFilePath} --bundle --platform=node --format=esm --outfile=${bundlePath} --external:@aws-sdk/client-s3 --external:@aws-sdk/s3-request-presigner`,
         { cwd: path.resolve(__dirname, '..'), stdio: 'pipe' }
       );
     } catch (e) {
@@ -100,7 +100,7 @@ console.log(JSON.stringify(result));
     expect(body).toEqual({ message: 'Hello from ESM bundle' });
   });
 
-  it('should work with CommonJS require (backward compatibility)', () => {
+  it('should work with CommonJS require (backward compatibility)', async () => {
     const api = require('../index.js');
     expect(typeof api).toBe('function');
 
@@ -109,6 +109,29 @@ console.log(JSON.stringify(result));
     expect(typeof app.get).toBe('function');
     expect(typeof app.post).toBe('function');
     expect(typeof app.run).toBe('function');
+
+    // Test full end-to-end functionality with CommonJS
+    app.get('/test-commonjs', (req, res) => {
+      res.json({ message: 'CommonJS works', method: req.method });
+    });
+
+    const event = {
+      httpMethod: 'GET',
+      path: '/test-commonjs',
+      headers: {},
+      body: null,
+      isBase64Encoded: false,
+    };
+
+    const result = await app.run(event, {});
+    
+    expect(result).toHaveProperty('statusCode', 200);
+    expect(result).toHaveProperty('headers');
+    expect(result.headers).toHaveProperty('content-type', 'application/json');
+    expect(result).toHaveProperty('body');
+
+    const body = JSON.parse(result.body);
+    expect(body).toEqual({ message: 'CommonJS works', method: 'GET' });
   });
 
   it('should work with ESM import', async () => {
@@ -137,4 +160,82 @@ console.log(JSON.stringify({
     const result = JSON.parse(output.trim());
     expect(result.isFunction).toBe(true);
   });
+
+  it('should bundle with esbuild for CommonJS without breaking (backward compatibility)', () => {
+    // Create a test entry file that requires from the CommonJS entry point
+    const testCode = `
+const api = require('${path.resolve(__dirname, '../index.js')}');
+
+const app = api();
+
+app.get('/test', (req, res) => {
+  res.json({ message: 'Hello from CommonJS bundle' });
+});
+
+module.exports.handler = async (event, context) => {
+  return await app.run(event, context);
+};
+`;
+
+    fs.writeFileSync(testFilePath, testCode);
+
+    const cjsBundlePath = path.join(tempDir, 'bundle-cjs.js');
+
+    // Bundle with esbuild using CommonJS format (mark AWS SDK as external since they're peer dependencies)
+    try {
+      execSync(
+        `npx esbuild ${testFilePath} --bundle --platform=node --format=cjs --outfile=${cjsBundlePath} --external:@aws-sdk/client-s3 --external:@aws-sdk/s3-request-presigner`,
+        { cwd: path.resolve(__dirname, '..'), stdio: 'pipe' }
+      );
+    } catch (e) {
+      throw new Error(`CommonJS bundling failed: ${e.message}`);
+    }
+
+    // Verify the bundle was created
+    expect(fs.existsSync(cjsBundlePath)).toBe(true);
+
+    // Test that the bundle executes without errors
+    const testEvent = JSON.stringify({
+      httpMethod: 'GET',
+      path: '/test',
+      headers: {},
+      body: null,
+      isBase64Encoded: false,
+    });
+
+    const testScript = `
+const { handler } = require('${cjsBundlePath}');
+const event = ${testEvent};
+handler(event, {}).then(result => {
+  console.log(JSON.stringify(result));
+}).catch(err => {
+  console.error(err.message);
+  process.exit(1);
+});
+`;
+
+    const scriptPath = path.join(tempDir, 'test-run-cjs.js');
+    fs.writeFileSync(scriptPath, testScript);
+
+    let output;
+    try {
+      output = execSync(`node ${scriptPath}`, {
+        encoding: 'utf-8',
+        cwd: tempDir,
+      });
+    } catch (e) {
+      throw new Error(`CommonJS bundle execution failed: ${e.message}\n${e.stderr}`);
+    }
+
+    const result = JSON.parse(output.trim());
+
+    // Verify the response
+    expect(result).toHaveProperty('statusCode', 200);
+    expect(result).toHaveProperty('headers');
+    expect(result.headers).toHaveProperty('content-type', 'application/json');
+    expect(result).toHaveProperty('body');
+
+    const body = JSON.parse(result.body);
+    expect(body).toEqual({ message: 'Hello from CommonJS bundle' });
+  });
 });