[Feature] Implement Comprehensive Unit Testing using Pytest

[knoxiboy]

Description
The tests/ directory exists, but many mini-projects lack proper test coverage. A robust project needs automated tests to ensure scripts don't break as new features are added.

Implementation

1. Add pytest to requirements.txt.
2. Write unit tests for core logical components of the scripts in the math/ and utilities/ folders (e.g., testing the expression evaluator, or string manipulation utilities).
3. Use unittest.mock to mock network calls or file I/O operations.
4. Configure a coverage tool (pytest-cov) to generate a test coverage report, aiming for >80% on tested modules.

Level: Critical
Affected Files: tests/, requirements.txt

[knoxiboy]

/assign gssoc'26
@steam-bell-92 Please assigne this issue to me.

[github-actions]

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[aaniya22]

pls assign this to me under gssoc

[knoxiboy]

/assign

[sam-dwdkr404]

Hi! @steam-bell-92
I am a GSSoC'26 contributor. I reviewed the issue and would like to work on fixing it. Could you please assign it to me? Thank you!