test: Implement comprehensive test coverage for all modules (past and future)

[coderabbitai]

Overview

This issue tracks the implementation of a comprehensive test suite for the entire syncup backend, covering all existing modules as well as any new modules added in future PRs.

---

Background

Raised during review of PR #22 (feat(tasks): Implement task CRUD API endpoints).
Original review comment: #22 (comment)

Requested by: @Zafar7645

---

Scope

Existing Modules to Cover

Module	Controller Spec	Service Spec	Notes
auth	auth.controller.spec.ts	auth.service.spec.ts	Already has basic spec; expand with full coverage
users	users.controller.spec.ts	users.service.spec.ts	Already has basic spec; expand with full coverage
projects	projects.controller.spec.ts	projects.service.spec.ts	Verify/expand coverage
board-columns	board-columns.controller.spec.ts	board-columns.service.spec.ts	Needs mocked providers; currently uses concrete service
tasks	tasks.controller.spec.ts	tasks.service.spec.ts	Needs mocked providers; currently uses concrete service

Testing Standards to Follow

• Controller specs: Use useValue mocks for all service dependencies (avoid injecting concrete services with TypeORM repository dependencies). Stub all public service methods with jest.fn().
• Service specs: Use getRepositoryToken() and useValue mocks for all TypeORM repository dependencies.
• Coverage targets: Happy path + key error paths (e.g., NotFoundException, ForbiddenException, UnauthorizedException).
• Guard testing: Mock JwtAuthGuard where needed in controller tests.

Future Modules

Any new module added to the project should include:

• A controller spec with mocked service providers.
• A service spec with mocked repository providers.
• Tests for all public methods covering both success and error cases.

---

Acceptance Criteria

• All controller specs use useValue mocks instead of concrete service classes.
• All service specs use mocked TypeORM repositories via getRepositoryToken().
• Each public method in every service has at least one success-path and one error-path test.
• Each controller handler has at least one test verifying correct delegation to the service mock.
• Tests pass in CI without requiring a live database connection.
• This checklist is updated as new modules are introduced.