Added a test for chaning the delimiter
Added test that checks if the string contains negative numbers
Created test for negative numbers
Refactored hasNegative function and added test for number bigger then 1000
Refactored check for number higher then 1000 and created test for delimiter of any length
Refactored test for delimiter of any length and added test for many delimiters
Refactored method getDelimiter and added a test for many delimiters of any length