Refactor test files for improved readability and consistency

- Removed unnecessary blank lines and adjusted formatting in test files.
- Ensured consistent use of commas in function calls and assertions across various test cases.
- Updated import statements for better organization and clarity.
- Enhanced mock setups in tests for better isolation and reliability.
- Improved assertions to follow a consistent style for better readability.

tests/conftest.py

@@ -13,10 +13,8 @@ from sqlmodel import SQLModel, select
 from sqlmodel.ext.asyncio.session import AsyncSession
 
 from app.core.database import get_db
-from app.models.credit_transaction import CreditTransaction  # Ensure model is imported for SQLAlchemy
 from app.models.plan import Plan
 from app.models.user import User
-from app.models.user_oauth import UserOauth  # Ensure model is imported for SQLAlchemy
 from app.utils.auth import JWTUtils, PasswordUtils