[Feature] Add Unit Tests

[sreedevk]

Is your feature request related to a problem? Please describe.
In order to avoid fixed issues from resurfacing, unit tests need to be added for each mod.

Describe the solution you'd like
Add Tests for:

• hashing
• file scanning
• finding duplicates by size
• finding duplicates by hashes
• printing output (integration tests)
• interactive mode (integration tests)

Describe alternatives you've considered
N/A

Additional context
As the application is going through major changes, it's essential to make sure that it doesn't break.