###### tags: `kata` # 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 ## Part 2: interact with external systems ### Add logging Add Logging Abilities to your new String Calculator (to an **`ILogger.Write()`**) interface (you will need a mock). Every time you call **`Add()`**, the sum result will be logged to the logger. When calling **`Add()`** and the logger throws an exception, the string calculator should notify an `IWebservice` of some kind that logging has failed with the message from the logger's exception (you will need a mock and a stub). ### A More Difficult Variation of the Kata 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"`**. Note that `scalc` is the name of the app executable. Then, 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 press enter (i.e. empty string): in that case it will exit. --- ## 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](http://osherove.com/tdd-kata-1) for the original idea.