Issue with Jest Testing in Express App using ES Modules
I’m currently working on testing my Express app using Jest with ES Modules, but I am encountering a few issues during the test run.
The Problems:
-
require is not defined — This error occurs when I try to mock my services using jest.mock(). Since I’m using ES modules (type: "module"), I can’t use require, and I’m unsure how to properly mock the services with ES module syntax.
-
Validation Error:
Option `extensionsToTreatAsEsm: ['.js']` includes '.js' which is always inferred.
I added extensionsToTreatAsEsm: [‘.js’] in Jest’s config to ensure .js files are treated as ES modules, but Jest is throwing this validation error, indicating it should be inferred automatically.
My Setup:
Node version: v18.20.4
Jest version: ^29.7.0
ESM support: Enabled with “type”: “module” in my package.json.
Configuration Files:
jest.config.js:
export default {
transform: {
'^.+\.js$': 'babel-jest', // Using babel-jest to handle ES module transformation
},
testEnvironment: 'node', // Set test environment to Node.js
moduleFileExtensions: ['js', 'mjs'], // Include ES module extensions
moduleNameMapper: {
'^(\.{1,2}/.*)\.js$': '$1', // Map file extensions correctly for ESM
},
};
babel.config.js:
export default {
presets: [
['@babel/preset-env', { targets: { node: 'current' } }], // Use Babel to transpile ES6+ code for current Node version
],
};
Test File (studentController.test.js):
import { jest } from '@jest/globals';
import request from 'supertest'; // Using supertest to test HTTP endpoints
import app from '../server.js'; // Importing the Express server
import {
fetchStudentsByTeacherId,
fetchStudentById,
createNewStudent,
updateExistingStudent,
processFileUpload
} from '../services/studentService.js'; // Importing services
// Mock the service layer with ES module syntax
jest.mock('../services/studentService.js', () => ({
fetchStudentsByTeacherId: jest.fn(),
fetchStudentById: jest.fn(),
createNewStudent: jest.fn(),
updateExistingStudent: jest.fn(),
processFileUpload: jest.fn(),
}));
describe('Student Controller', () => {
describe('getStudentsByTeacher', () => {
it('should fetch students for a teacher by teacher ID', async () => {
const mockStudents = [{ firstName: 'John', lastName: 'Doe' }];
fetchStudentsByTeacherId.mockResolvedValue(mockStudents);
const res = await request(app).get('/students/by-teacher/teacher123');
expect(res.status).toBe(200);
expect(res.body).toEqual(mockStudents);
expect(fetchStudentsByTeacherId).toHaveBeenCalledWith('teacher123');
});
it('should return 500 if an error occurs', async () => {
fetchStudentsByTeacherId.mockRejectedValue(new Error('Failed to fetch students'));
const res = await request(app).get('/students/by-teacher/teacher123');
expect(res.status).toBe(500);
expect(res.body.message).toBe('Server error');
});
});
describe('getStudentById', () => {
it('should fetch a student by student ID', async () => {
const mockStudent = { firstName: 'John', lastName: 'Doe' };
fetchStudentById.mockResolvedValue(mockStudent);
const res = await request(app).get('/students/student123');
expect(res.status).toBe(200);
expect(res.body).toEqual(mockStudent);
expect(fetchStudentById).toHaveBeenCalledWith('student123');
});
it('should return 500 if an error occurs', async () => {
fetchStudentById.mockRejectedValue(new Error('Failed to fetch student'));
const res = await request(app).get('/students/student123');
expect(res.status).toBe(500);
expect(res.body.message).toBe('Server error');
});
});
describe('addStudent', () => {
it('should add a new student and return a success message', async () => {
const mockStudent = { firstName: 'John', lastName: 'Doe' };
createNewStudent.mockResolvedValue(mockStudent);
const studentData = {
firstName: 'John',
lastName: 'Doe',
rollNumber: 123,
class: 'class123',
guardians: [{ firstName: 'Jane', isPrimaryContact: true }],
photo: 'url',
};
const res = await request(app).post('/students/add').send(studentData);
expect(res.status).toBe(201);
expect(res.body.message).toBe('Student and guardians added successfully');
expect(res.body.student).toEqual(mockStudent);
expect(createNewStudent).toHaveBeenCalledWith(studentData);
});
it('should return 500 if an error occurs', async () => {
createNewStudent.mockRejectedValue(new Error('Failed to add student'));
const studentData = {
firstName: 'John',
lastName: 'Doe',
rollNumber: 123,
class: 'class123',
guardians: [{ firstName: 'Jane', isPrimaryContact: true }],
photo: 'url',
};
const res = await request(app).post('/students/add').send(studentData);
expect(res.status).toBe(500);
expect(res.body.message).toBe('Error adding student');
});
});
describe('updateStudent', () => {
it('should update a student and return a success message', async () => {
const mockUpdatedStudent = { firstName: 'John', lastName: 'Doe', rollNumber: 123 };
updateExistingStudent.mockResolvedValue(mockUpdatedStudent);
const studentData = {
firstName: 'John',
lastName: 'Doe',
rollNumber: 123,
class: 'class123',
guardians: [{ firstName: 'Jane', isPrimaryContact: true }],
photo: 'url',
};
const res = await request(app).put('/students/edit/student123').send(studentData);
expect(res.status).toBe(200);
expect(res.body.message).toBe('Student and guardians updated successfully');
expect(res.body.student).toEqual(mockUpdatedStudent);
expect(updateExistingStudent).toHaveBeenCalledWith('student123', studentData);
});
it('should return 500 if an error occurs', async () => {
updateExistingStudent.mockRejectedValue(new Error('Failed to update student'));
const studentData = {
firstName: 'John',
lastName: 'Doe',
rollNumber: 123,
class: 'class123',
guardians: [{ firstName: 'Jane', isPrimaryContact: true }],
photo: 'url',
};
const res = await request(app).put('/students/edit/student123').send(studentData);
expect(res.status).toBe(500);
expect(res.body.message).toBe('Error updating student');
});
});
describe('uploadStudentFile', () => {
it('should process the student file upload and return a success message', async () => {
processFileUpload.mockResolvedValue();
const res = await request(app).post('/students/upload-student-file').send({ fileUrl: 'https://s3.amazonaws.com/file.csv' });
expect(res.status).toBe(200);
expect(res.body.message).toBe('Student file notification received, processing will start shortly.');
expect(processFileUpload).toHaveBeenCalledWith('https://s3.amazonaws.com/file.csv', 'BULK_IMPORT_STUDENTS');
});
it('should return 500 if an error occurs', async () => {
processFileUpload.mockRejectedValue(new Error('Failed to process file'));
const res = await request(app).post('/students/upload-student-file').send({ fileUrl: 'https://s3.amazonaws.com/file.csv' });
expect(res.status).toBe(500);
expect(res.body.message).toBe('Error processing student file notification');
});
});
});
What I’ve Tried:
I’m using Jest with babel-jest to transform ES modules, and I’ve set up Babel to transpile ES6+ for the current Node version.
I included extensionsToTreatAsEsm: [‘.js’] in jest.config.js because I’m working with ES modules (type: “module” in my package.json).
Questions:
How can I mock the services in Jest when using ES modules?
How do I resolve the validation error related to extensionsToTreatAsEsm?
