Add tests for /signin endpoint

[mridxl]

What is this issue related to?

Enhancement

Description

This issue involves writing comprehensive unit tests for the /signin endpoint to ensure it handles various scenarios correctly, including valid and invalid credentials, missing fields, and server errors.

Expected Behavior

The tests should verify that:

• The endpoint returns a valid token cookie upon successful authentication.
• The endpoint returns an appropriate error message for invalid credentials.
• The endpoint handles missing or malformed input fields correctly.
• The endpoint responds with the correct status codes for different scenarios.

Current Behavior

Currently, there is only one test for the /signin endpoint

Additional Information (optional)

No response

Confirmation Checklist

• I have searched for similar issues before creating this one.
• I have provided all the necessary information to understand and reproduce the issue.