Unit test auth

[KAMALDEEN333]

Generated a comprehensive Unit Tests for auth.service.ts

Description

Summary
Title: Generate Unit Tests for auth.service.ts in test/auth/auth.service.spec.ts
The user module already exists, but it currently lacks unit tests for the service layer.
This issue is to generate a complete test suite for auth.service.ts.

Task
Navigate to:

test/auth/
Create the test file:
auth.services.spec.ts
Implement unit tests covering:
All public methods in auth.service.ts
Expected success flows
Expected failure/error scenarios
Mocking dependencies such as:
Repositories
External services (if any)
Testing Requirements
Use Jest as the testing framework (default for NestJS).
Use TestingModule with mocked providers.
Ensure 90%+ coverage for user.service.ts.
Tests should be isolated, not touching database or integration logic.

closes #51

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