Test for rejects empty string and nonzero span requires message "Series length must be less than or equal to the length of the string to search." with length 1, but message "String should contain only digits" is more satiable because String is used in the constructor and cannot be used anywhere dispute of the length.
Test for rejects empty string and nonzero span requires message "Series length must be less than or equal to the length of the string to search." with length 1, but message "String should contain only digits" is more satiable because String is used in the constructor and cannot be used anywhere dispute of the length.