Addition of a comprehensive suite of unit tests, which significantly enhances the reliability and correctness of the extension. 
- testPreparePageData(): Validates the correct preparation of page data.
- testAnalyzePages(): Checks the complete page analysis process.
- testCalculateSimilarity(): Ensures accurate similarity calculations between pages.
- testFindCommonKeywords(): Verifies the detection of common keywords.
- testDetermineRelevance(): Confirms correct relevance level assignments.