🧪 Implement Automated Testing Suite

## Description
Add comprehensive tests to ensure code reliability.

## Tasks
- [ ] Set up pytest framework
- [ ] Write unit tests for core functions
- [ ] Add integration tests
- [ ] Test with various file formats
- [ ] Achieve 70%+ code coverage
- [ ] Set up CI/CD with GitHub Actions

## Expected Outcome
Automated test suite ensuring code quality.

## Skills Required
- Python testing
- pytest
- CI/CD
- GitHub Actions

## Difficulty Level
🟡 Intermediate

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*Hacktoberfest 2025 - Testing*

No files, tests, or entry points are named. Start by locating the core functions and supported file-format handling, then determine how pytest and GitHub Actions fit the repository; done means unit and integration tests cover the requested formats and the project reaches at least 70% coverage in CI.

Written by the indexing model from the issue text.