Test: 201, and test name is refactored to "hundreds and single digit convert to three words"
TPP: constant -> scala (1 -> number / 100)
all other code changes are refactorings, including merging the if condition (number == 201) and refactor "number - 100" to "number % 100" which get the single digit number.
Test: 121
TPP: expression -> function ( NUMBER_TO_ONE_WORD.get(number % 100) -> convertWithinCountingUnit(number % 100) )