Homework 12: Service Unit-Test

🧩 Task Definition

Complete all service-level unit tests for the EmployeesService. Update EmployeesService.test.ts so that each service method (except save) is covered.

Your task includes:

• ✅ Write tests for getAll, getEmployee, addEmployee, updateEmployee, and deleteEmployee.
• ✅ Use beforeEach(resetTestEmployees) to reset the service state before every test.
• ✅ Test for all expected success and error cases (NotFoundError, AlreadyExistsError).
• ✅ Ensure all tests pass.

Run tests

npm run test-service map

All tests must pass ✅

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📝 Description

This homework implements unit tests for the EmployeesService module, responsible for CRUD operations on employee data. The service is tested independently from the Express API and focuses solely on business logic and data handling.

Each test verifies:

• Proper data retrieval and filtering.
• Correct employee addition, updates, and deletions.
• Proper error throwing for non-existing or duplicate employees.
• Stable state before each test run.

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🎯 Purpose

The goal is to practice isolated unit testing of service logic, ensuring that business rules work as expected without involving routes or controllers.

By the end you should:

• Understand how to structure service tests in TypeScript.
• Use node:test and assert/strict for validation.
• Apply test data reset to maintain consistent test environments.
• Detect logical or state management errors early.

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✨ Features

• 🧩 Unit tests for all EmployeesService methods.
• 🧱 Independent of Express controllers or routes.
• ⚙️ Pre-defined test data set (stateEmployees) for repeatable scenarios.
• 🔁 beforeEach environment reset with resetTestEmployees().
• 🚨 Error handling tests for AlreadyExistsError and NotFoundError.
• 🧠 Written in TypeScript using modern Node.js test API.

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🔍 How It Works

1. Service Initialization EmployeesServiceMap loads a predefined in-memory collection of employees.

2. Test Environment Setup The resetTestEmployees() utility clears the current employees and re-adds a fresh copy of stateEmployees before each test block.

3. Grouped Test Cases

   • employeesGetTestCases → tests for retrieving data.
   • employeesAddTestCases → tests for adding employees.
   • employeesUpdateTestCases → tests for updates.
   • employeesDeleteTestCases → tests for deletion.

4. Assertions

   • Uses assert.rejects() for error cases.
   • Uses assert.deepEqual() and assert.ok() for data comparison.
   • Validates object equality and state consistency.

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📜 Output Example

✅ All tests pass

✔ Add existing employee -> throwing AlreadyExistsError
✔ Add new employee object with no id -> returns added object with id
✔ Delete non existing employee -> throws NotFoundError
✔ Delete existing employee
✔ Get non existing employee by ID -> throws NotFoundError
✔ Get all employee objects -> returns all state employees
✔ Get all employees by department -> filters correctly
✔ Get existing employee -> returns employee
✔ Update non existing employee -> throws NotFoundError
✔ Update existing employee -> returns employee with updated salary value

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📦 Usage

1️⃣ Install dependencies

npm install

2️⃣ Run the service unit tests

npm run test-service map

3️⃣ Inspect results All tests should display a ✅ status and no failures.

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🚀 Usage Examples (HTTP)

(Optional — for context with controller integration)

# Fetch all employees
curl -X GET http://localhost:3000/employees

# Add new employee
curl -X POST http://localhost:3000/employees \
-H "Content-Type: application/json" \
-d '{"fullName":"John Doe","department":"QA","salary":10000,"birthDate":"2000-01-01","avatar":"https://example.com"}'

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🗂 Project Structure

src/
├── __tests__/
│   └── serviceTests/
│       ├── EmployeesService.test.ts
│       ├── testCases/
│       │   ├── employeesGet.test.ts
│       │   ├── employeesAdd.test.ts
│       │   ├── employeesUpdate.test.ts
│       │   └── employeesDelete.test.ts
│       ├── employeesData/
│       │   └── employeesData.ts
│       └── utils/
│           └── setupTestEnv.ts
├── service/
│   ├── employee/
│   │   ├── EmployeesService.ts
│   │   ├── EmployeesServiceMap.ts
│   │   └── EmployeesServiceMock.test.ts
│   ├── accounting/
│   └── registry.ts
└── model/
    └── errorTypes/

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✅ Dependencies

Package	Purpose
node:test	Built-in test framework for unit tests
assert/strict	Assertion library for equality and error checks
lodash	Used for array comparison and utility functions
uuid	Generates unique employee IDs
TypeScript	Static typing and compiler support
dotenv	Environment configuration
winston	Structured logging utility

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📄 License

MIT License

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🧮 Conclusion

Homework #12 focuses on ensuring that the EmployeesService business logic is fully tested and reliable. By testing each method individually, the project achieves:

• Consistent data handling across CRUD operations.
• Predictable behavior for edge cases and errors.
• Clean, maintainable unit tests that can serve as templates for future services.

All tests ✅ passed — the service is solid and ready for integration with controllers and routes.

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Made with ❤️ and TypeScript by Sam-Shepsl Malikin