fix: throw error and add tests for ReverseNumber

[vil02]

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Describe your change:

Errors should be thrown not returned. This PR also adds tests. I do not want to specify how the ReverseNumber should react to negative inputs, so I did not tests covering such situation.

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new JavaScript files are placed inside an existing directory.
• All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames.
  Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1ea7a5c) 83.47% compared to head (aaea118) 83.62%.

Additional details and impacted files

@@ Coverage Diff @@## master #1608 +/- ## ========================================== + Coverage 83.47% 83.62% +0.14%  ========================================== Files 377 377 Lines 19745 19745 Branches 2907 2912 +5 ========================================== + Hits 16482 16511 +29 + Misses 3263 3234 -29 

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