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String Calculator Kata

The following is a TDD Kata, an exercise in coding, refactoring and test-first, that you should apply daily for at least 15-30 minutes.

Before you start

  • Try not to read ahead.
  • Do one task at a time. The trick is to learn to work incrementally.
  • Make sure you only test for correct inputs. There is no need to test for invalid inputs for this kata.

The kata

Step 1: the simplest thing

Create a simple String calculator with a method int add(String numbers).

  • The string argument can contain 0, 1 or 2 numbers, and will return their sum (for an empty string it will return 0) for example "" or "1" or "1,2".
  • Start with the simplest test case of an empty string and move to 1 and two numbers.
  • 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.

Step 2: handle an unknown amount of numbers

Allow the add() method to handle an unknown amount of numbers.

Step 3: handle new lines between numbers

Allow the add() method to handle new lines between numbers (instead of commas).

  • the following input is ok: "1\n2,3" (will equal 6)
  • the following input is NOT ok: "1,\n" (not need to prove it - just clarifying)

Step 4: support different delimiters

Support different delimiters: 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 3 where the default delimiter is ';'.

The first line is optional. All existing scenarios should still be supported.

Step 5: negative numbers

Calling add() with a negative number will throw an exception "negatives not allowed" - and the negative that was passed.

For example add("1,4,-1") should throw an exception with the message "negatives not allowed: -1".

If there are multiple negatives, show all of them in the exception message.

Step 6: ignore big numbers

Numbers bigger than 1000 should be ignored, so adding 2 + 1001 = 2

General requirements

  • Use whatever language and frameworks you want. Use something that you know well.
  • Provide a README with instructions on how to compile and run the application.

IMPORTANT: Implement the requirements focusing on writing the best code you can produce.

CODE SUBMISSION: Add the code to your own Github account and send us the link.

Credits to Roy Osherove for the original idea.