test: added tests for Decimal Isolate function

[HRIDYANSHU054]

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Describe your change:

• Add an algorithm?
  Added tests for Maths/DecimalIsolate function and extended comments about its usage

Before:

/*  * function isolates the decimal part of a number.  * Take the number and subtract it from the floored number.  * Return the result.  */

Now:

/*  * This function isolates the decimal part of a number.  * - If input is a number or a numeric string, it isolates and returns the decimal part.  * - If input is an array:  * - It isolates the decimal part of the first element.  * - If the array contains more than one element, only the first element is considered.  * - If the array is empty, it returns 0.  * - If input is not a number, a numeric string, or a valid first element array,  * the function returns 0.  */

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 ✅

Project coverage is 84.81%. Comparing base (ff314a2) to head (053800f).
Report is 1 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@ ## master #1752 +/- ## ========================================== + Coverage 84.76% 84.81% +0.05%  ========================================== Files 378 378 Lines 19742 19743 +1 Branches 2955 2956 +1 ========================================== + Hits 16735 16746 +11  + Misses 3007 2997 -10 

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