Test: Added tests to increase test coverage of models

[Rkejji]

Description

Added unit test to models while mocking API calls to the real openai API.

Motivation and Context

This PR is related to this issue #1513

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds core functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)
• Example (update in the folder of example)

Implemented Tasks

• Subtask 1
• Subtask 2
• Subtask 3

Checklist

Go over all the following points, and put an x in all the boxes that apply.
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• I have read the CONTRIBUTION guide. (required)
• My change requires a change to the documentation.
• I have updated the tests accordingly. (required for a bug fix or a new feature)
• I have updated the documentation accordingly.

[Wendong-Fan]

thanks @Rkejji for the great contribution!
for deepseek model we removed the part so now there's one error to be fixed:
https://github.com/camel-ai/camel/actions/runs/13228863991/job/36923215735?pr=1550
could you look into this part and let me know if there's anything I can support~

[Rkejji]

thanks @Rkejji for the great contribution! for deepseek model we removed the part so now there's one error to be fixed: https://github.com/camel-ai/camel/actions/runs/13228863991/job/36923215735?pr=1550 could you look into this part and let me know if there's anything I can support~

It is done, the issue was due to the fact that the GET_REASONING_CONTENT env variable was not declared in the CI. I declared it in the test let me know if you prefer to have it in the CI instead.