Add module loading tests for user function

.gitignore

@@ -48,3 +48,7 @@ dist/
 
 # Stores VSCode versions used for testing VSCode extensions
 .vscode-test
+
+deps/artifacts/
+deps/aws-lambda-cpp*/
+deps/curl*/

test/handlers/extensionless/esm-extensionless

@@ -0,0 +1,6 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+// This should fail because it's ESM syntax in a CJS context
+export const handler = async (event) => {
+    return "This should fail";
+};

test/handlers/extensionless/index

@@ -0,0 +1,8 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+// This is a CommonJS module without file extension
+
+module.exports.handler = async (event) => {
+    return "Hello from extensionless CJS";
+};

test/handlers/pkg-less/cjsAndMjs.js

@@ -0,0 +1,9 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+import { someESMFunction } from './esmModule.js';  // ESM import
+
+module.exports.handler = async (event) => {  // CJS export
+    return someESMFunction(event);
+};
+
+export const esm = 'This is ESM syntax';  // ESM export

test/handlers/pkg-less/cjsImportCjs.js

@@ -0,0 +1,9 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+
+const { getMessage } = require('./cjsModule.cjs')
+
+exports.handler = async (_event) => {
+  return getMessage();
+}

test/handlers/pkg-less/cjsImportESM.cjs

@@ -0,0 +1,10 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+
+// This static import is not allowed in CJS
+import { getMessage } from './esmModule';
+
+module.exports.handler = async () => {
+    return getMessage();
+};

test/handlers/pkg-less/cjsInMjs.mjs

@@ -0,0 +1,8 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+
+// This should fail because it's CJS syntax in a ESM context
+module.exports.handler = async (_event) => {
+  return 'This should fail';
+};

test/handlers/pkg-less/cjsModule.cjs

@@ -0,0 +1,7 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+
+module.exports.getMessage = () => {
+    return "Hello from CJS!";
+};

test/handlers/pkg-less/esmImportCjs.mjs

@@ -0,0 +1,7 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+import { getMessage } from './cjsModule.cjs';
+
+export const handler = async (_event) => {
+    return getMessage();
+};

test/handlers/pkg-less/esmInCjs.cjs

@@ -0,0 +1,6 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+// This should fail because it's ESM syntax in a CJS context
+export const handler = async (_event) => {
+  return 'This should fail';
+};

test/handlers/pkg-less/esmModule.js

@@ -0,0 +1,9 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+export const handler = async (_event) => {
+  return 'Hello from ESM.js';
+};
+
+export const getMessage = () => {
+  return "Hello from ESM!";
+};

test/handlers/pkg-less/esmRequireCjs.mjs

@@ -0,0 +1,7 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+const { getMessage } = require('./cjsModule.cjs')
+
+export const handler = async (_event) => {
+    return getMessage();
+};

test/handlers/pkg/type-cjs/cjs

@@ -0,0 +1,8 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+// This is a CommonJS module without file extension
+
+module.exports.handler = async (event) => {
+    return "Hello from extensionless CJS";
+};

test/handlers/pkg/type-cjs/cjsModule.js

@@ -0,0 +1,7 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+
+module.exports.handler = async (_event) => {
+  return 'Hello from CJS.js';
+};

test/handlers/pkg/type-cjs/esm

@@ -0,0 +1,6 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+// This should fail because it's ESM syntax in a CJS context
+export const handler = async (event) => {
+    return "This should fail";
+};

test/handlers/pkg/type-cjs/esmModule.js

@@ -0,0 +1,6 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+// This should fail because it's ESM syntax in a CJS context
+export const handler = async (_event) => {
+  return 'This should fail';
+};

test/handlers/pkg/type-cjs/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}

test/handlers/pkg/type-esm/cjs

@@ -0,0 +1,8 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+// This is a CommonJS module without file extension
+
+module.exports.handler = async (event) => {
+    return "Hello from extensionless CJS";
+};

test/handlers/pkg/type-esm/cjsModule.js

@@ -0,0 +1,8 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+'use strict';
+
+// This should fail because it's CJS syntax in a ESM context
+module.exports.handler = async (_event) => {
+  return 'This should fail';
+};

test/handlers/pkg/type-esm/esm

@@ -0,0 +1,6 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+// This should fail because it's ESM syntax in a CJS context
+export const handler = async (event) => {
+    return "This should fail";
+};

test/handlers/pkg/type-esm/esmModule.js

@@ -0,0 +1,5 @@
+/** Copyright 2025 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
+
+export const handler = async (_event) => {
+  return 'Hello from ESM.js';
+};

test/handlers/pkg/type-esm/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}

test/unit/UserFunctionTest.js

@@ -10,6 +10,7 @@ const {
   HandlerNotFound,
   ImportModuleError,
   MalformedHandlerName,
+  UserCodeSyntaxError,
 } = require('lambda-runtime/Errors.js');
 const UserFunction = require('lambda-runtime/UserFunction.js');
 
@@ -250,6 +251,166 @@ describe('UserFunction.load method', () => {
 
     response.should.be.resolvedWith('moon');
   });
+
+  it('should successfully load a CJS handler from extensionless file (no package.json)', async () => {
+    const handler = await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'extensionless'),
+      'index.handler',
+    );
+    const response = await handler('test event');
+
+    response.should.equal('Hello from extensionless CJS');
+  });
+
+  it('should fail to load ESM syntax from extensionless file (no package.json)', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'extensionless'),
+      'esm-extensionless.handler',
+    ).should.be.rejectedWith(UserCodeSyntaxError);
+  });
+
+  it('should load CJS handler from extensionless file with type:commonjs', async () => {
+    // package.json is ignored in the case of extensionless
+    const handler = await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg', 'type-cjs'),
+      'cjs.handler',
+    );
+    const response = await handler('test event');
+
+    response.should.equal('Hello from extensionless CJS');
+  });
+
+  it('should fail to load ESM handler from extensionless file with type:commonjs', async () => {
+    // package.json is ignored in the case of extensionless
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg', 'type-cjs'),
+      'esm.handler',
+    ).should.be.rejectedWith(UserCodeSyntaxError);
+  });
+
+  it('should load CJS handler from extensionless file with type:module', async () => {
+    // package.json is ignored in the case of extensionless
+    const handler = await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg', 'type-esm'),
+      'cjs.handler',
+    );
+    const response = await handler('test event');
+
+    response.should.equal('Hello from extensionless CJS');
+  });
+
+  it('should fail to load ESM handler from extensionless file with type:module', async () => {
+    // package.json is ignored in the case of extensionless
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg', 'type-esm'),
+      'esm.handler',
+    ).should.be.rejectedWith(UserCodeSyntaxError);
+  });
+
+  it('should load CJS handler from JS file with type:commonjs', async () => {
+    const handler = await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg', 'type-cjs'),
+      'cjsModule.handler',
+    );
+    const response = await handler('test event');
+
+    response.should.equal('Hello from CJS.js');
+  });
+
+  it('should fail to load ESM handler from JS file with type:commonjs', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg', 'type-cjs'),
+      'esmModule.handler',
+    ).should.be.rejectedWith(UserCodeSyntaxError);
+  });
+
+  it('should load ESM handler from JS file with type:module', async () => {
+    const handler = await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg', 'type-esm'),
+      'esmModule.handler',
+    );
+    const response = await handler('test event');
+
+    response.should.equal('Hello from ESM.js');
+  });
+
+  it('should fail to load CJS handler from JS file with type:module', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg', 'type-esm'),
+      'cjsModule.handler',
+    ).should.be.rejectedWith(
+      ReferenceError,
+      /module is not defined in ES module scope/,
+    );
+  });
+
+  it('should fail to load ESM handler from JS file without type context', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg-less'),
+      'esmModule.handler',
+    ).should.be.rejectedWith(UserCodeSyntaxError);
+  });
+
+  it('should fail to load CJS handler from MJS file without type context', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg-less'),
+      'cjsInMjs.handler',
+    ).should.be.rejectedWith(
+      ReferenceError,
+      /module is not defined in ES module scope/,
+    );
+  });
+
+  it('should fail to load ESM handler from CJS file without type context', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg-less'),
+      'esmInCjs.handler',
+    ).should.be.rejectedWith(UserCodeSyntaxError);
+  });
+
+  it('should fail to load mixed context handler from JS file without type context', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg-less'),
+      'cjsAndMjs.handler',
+    ).should.be.rejectedWith(UserCodeSyntaxError);
+  });
+
+  it('should successfully load ESM handler importing from CJS', async () => {
+    const handler = await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg-less'),
+      'esmImportCjs.handler',
+    );
+
+    const response = await handler();
+    response.should.equal('Hello from CJS!');
+  });
+
+  it('should fail when CJS tries to import from ESM using static import', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg-less'),
+      'cjsImportESM.handler',
+    ).should.be.rejectedWith(UserCodeSyntaxError);
+  });
+
+  it('should successfully load CJS handler importing from CJS', async () => {
+    const handler = await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg-less'),
+      'cjsImportCjs.handler',
+    );
+
+    const response = await handler();
+    response.should.equal('Hello from CJS!');
+  });
+
+  it('should fail when using require in .mjs', async () => {
+    await UserFunction.load(
+      path.join(HANDLERS_ROOT, 'pkg-less'),
+      'esmRequireCjs.handler',
+    ).should.be.rejectedWith(
+      ReferenceError,
+      /require is not defined in ES module scope/,
+    );
+  });
 });
 
 describe('type guards HandlerFunction', () => {