👀 Views: 3 💬 Answers: 1 📅 Created: 2025-06-01

mocha sinon unit-testing javascript

I'm following best practices but I'm dealing with I'm performance testing and I'm optimizing some code but I'm stuck on something that should probably be simple..... I've been struggling with this for a few days now and could really use some help... I'm currently working on a Node.js application where I need to write unit tests for a service that interacts with a database through a repository pattern. I’m using Mocha as my testing framework along with Sinon for stubbing and mocking. The service function I want to test looks like this: ```javascript class UserService { constructor(userRepository) { this.userRepository = userRepository; } async getUserById(id) { if (!id) throw new Error('ID is required'); return await this.userRepository.findById(id); } } ``` And the repository looks like this: ```javascript class UserRepository { async findById(id) { // Simulate a database call return database.find(user => user.id === id); } } ``` My goal is to test the `getUserById` method by mocking the `UserRepository` to prevent actual database calls. However, I’m encountering an issue. Below is the test I have written: ```javascript const { expect } = require('chai'); const sinon = require('sinon'); const UserService = require('./UserService'); const UserRepository = require('./UserRepository'); describe('UserService', () => { let userService; let userRepositoryStub; beforeEach(() => { userRepositoryStub = sinon.createStubInstance(UserRepository); userService = new UserService(userRepositoryStub); }); it('should return user when ID is valid', async () => { const mockUser = { id: 1, name: 'John Doe' }; userRepositoryStub.findById.returns(Promise.resolve(mockUser)); const user = await userService.getUserById(1); expect(user).to.deep.equal(mockUser); }); }); ``` However, when I run this test, I receive the following error: ``` TypeError: userRepositoryStub.findById.returns is not a function ``` I've tried to investigate the way I create the stub instance. It seems like the `createStubInstance` may not be properly returning a stub for the method `findById`. I also checked the version of Sinon I'm using (`^11.1.2`). Am I missing something in the way I'm setting up my stubs? Any help would be greatly appreciated! Thanks in advance! Could this be a known issue? I'm working on a CLI tool that needs to handle this. What would be the recommended way to handle this? I'm on CentOS using the latest version of Javascript. Thanks for taking the time to read this! I'm working with Javascript in a Docker container on macOS.