String Calculator for Scala

This is a slight repurposing of the String Calculator kata on Roy Osherove’s website. I’ve updated it for my own impression of TDD, and for Scala notation and types, but many of the words are still arranged in Roy’s order.

Before you start:

• Try not to read ahead.
• Do one task at a time. The trick is to learn to work incrementally.
• Only test for correct inputs. there is no need to test for invalid inputs for this kata.
• Remember to solve things as simply as possible so that you force yourself to write tests you did not think about.
• Remember to refactor after each passing test.
• Do as much as you can in 30 minutes. Don’t worry if you don’t finish, improvements come from repetition.

String Calculator

1. Create a simple String calculator with a method
   add(number: String): Int
2. The method can take 0, 1 or 2 numbers separated by a comma, and will return their sum (for an empty string it will return 0) for example “” or “1” or “1,2”
3. Start with the simplest test case of an empty string and move to one and two numbers
4. Allow the Add method to handle an unknown amount of numbers
5. Allow the Add method to handle new lines between numbers (instead of commas).
6. the following input is ok: “1\n2,3” (will equal 6)
7. the following input is NOT ok: “1,\n” (no need to prove it — just clarifying)
8. Support different delimiters
9. to change a delimiter, the beginning of the string will contain a separate line that looks like this: “//[delimiter]\n[numbers…]” for example “//;\n1;2” should return three where the default delimiter is ‘;’ .
10. the first line is optional. all existing scenarios should still be supported
11. Calling Add with a negative number will cause an error state that shows the negative that was passed. If there are multiple negatives, show all of them in the exception message. Represent the error state using an Either
12. Numbers bigger than 1000 should be ignored, so adding 2 + 1001 = 2
13. Delimiters can be of any length with the following format: “//[delimiter]\n” for example: “//[***]\n1***2***3” should return 6
14. Allow multiple delimiters like this: “//[delim1][delim2]\n” for example “//[*][%]\n1*2%3” should return 6.
15. Make sure you can also handle multiple delimiters with length longer than one char