Refactor: comprehensive unit tests for FileUtils (Deletion, Validation & Storage)

[harshsomankar123-tech]

fixes #4713
Summary
This PR significantly improves the code coverage of FileUtils.kt by adding comprehensive unit tests for critical file operations, ZIM validation, and storage path resolution. It achieves >90% coverage for the file.

Changes

• Preserved Existing Tests: Kept the original tests for getAllZimParts to ensure no regression in split-archive detection.
• Added Deletion Logic: Added tests for deleteZimFile to verify correct removal of .zim, .part, and split chunks (.zimaa, etc.).
• Added Validation Logic: Added tests for isValidZimFile and isSplittedZimFile to validate file extensions and types.
• Added Storage & URI Logic: Added tests for getStoragePath and getLocalFilePathByUri using MockK to mock Android static classes (Environment, Uri, Context).

Technical Details

• Used mockkStatic to mock Kotlin extension functions and Android.os.Environment.
• Covered edge cases for file collision (e.g., when both book.zim and book.zim.part exist).
• Verified safety checks for file descriptors to prevent runtime crashes.

[atharvyadav22]

@harshsomankar123-tech i have recently changed File Utils please view that and add tests accordingly as i have made new features

[harshsomankar123-tech]

@atharvyadav22 Sure, I’ll update the tests accordingly

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.56%. Comparing base (0bf40b7) to head (9fe178a).
⚠️ Report is 32 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4721      +/-   ##
============================================
+ Coverage     60.48%   60.56%   +0.08%     
+ Complexity     1625     1619       -6     
============================================
  Files           327      330       +3     
  Lines         15615    15726     +111     
  Branches       2146     2162      +16     
============================================
+ Hits           9445     9525      +80     
- Misses         4731     4734       +3     
- Partials       1439     1467      +28     

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[harshsomankar123-tech]

@MohitMaliFtechiz could you please review this when you get time? Thanks!