TDD – getting started

It’s not TDD, it’s design by example

… I write a test that starts by ‘newing’ up a class that doesn’t exist. It won’t compile. (red) So, I create an empty class so it compiles, and succeeds. (green). I call a method on the class, it doesn’t yet exist and won’t compile. (red) I right click, “generate method”. Compile, run test, success. (green) I then write my assert line in my test. (red) I then start coding the method to get it to pass. (green). etc, etc, etc I didn’t lose anything, and each step was a few seconds, or minutes, so I won’t forget anything …

from here

Kata 1

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


String Calculator

  1. Create a simple String calculator with a method int Add(string numbers)
    1. The method can take 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”
    2. Start with the simplest test case of an empty string and move to 1 and two numbers
    3. Remember to solve things as simply as possible so that you force yourself to write tests you did not think about
    4. Remember to refactor after each passing test
  2. Allow the Add method to handle an unknown amount of numbers
  3. Allow the Add method to handle new lines between numbers (instead of commas).
    1. the following input is ok:  “1\n2,3”  (will equal 6)
    2. the following input is NOT ok:  “1,\n” (not need to prove it – just clarifying)
    1. Support different delimiters

    2. 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 ‘;’ .
    3. the first line is optional. all existing scenarios should still be supported
  4. Calling Add with a negative number will throw an exception “negatives not allowed” – and the negative that was passed.if there are multiple negatives, show all of them in the exception message

    stop here if you are a beginner. Continue if you can finish the steps so far in less than 30 minutes.

  5. Numbers bigger than 1000 should be ignored, so adding 2 + 1001  = 2
  6. Delimiters can be of any length with the following format:  “//[delimiter]\n” for example: “//[***]\n1***2***3” should return 6
  7. Allow multiple delimiters like this:  “//[delim1][delim2]\n” for example “//[*][%]\n1*2%3” should return 6.
  8. make sure you can also handle multiple delimiters with length longer than one char

Kata 2

  1. Everytime you call Add(string) it also outputs the number result of the calculation in a new line to the terminal or console. (remember to try and do this test first!)
  2. Create a program (test first)that uses string calculator, which the user can invoke through the terminal/console by calling “scalc ‘1,2,3’” and will output the following line before exiting: “The result is 6”
  3. Instead of exiting after the first result, the program will ask the user for “another input please” and print the result of the new user input out as well, until the user gives no input and just preses enter. in that case it will exit.