String Calculator Kata

The String Calculator Kata is a Test-Driven Development (TDD) kata—an exercise in coding, refactoring and test-first, that you should apply daily for at least 15 minutes.

Roy Osherove published the original version of the kata. The remainder of this document is a slightly cleaned-up and reformatted version of Roy's original work.

Instructions

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 valid inputs. There is no need to test for invalid inputs for this kata.
Test first!

Steps

Create a simple class StringCalculator with a public method with signature
```
 int Add(string numbers)
```
The string parameter numbers can contain up to two numbers, separated by commas. The method returns their sum. For an empty string the method returns 0. For example, the string "" returns 0, the string "1" returns 1, and the string "1,2" returns 3.

Hints:
- Start with the simplest test case of an empty string and then move to cases with one and two numbers.
- Remember to solve things as simple as possible so that you force yourself to write tests you did not think about.
- Remember to refactor after each passing test.
Allow the Add method to handle an unknown amount of numbers.
Allow the Add method to handle newlines between numbers (instead of commas).

For example, the string "1\n2,3" is valid input and returns 6. The string "1,\n" is invalid. Remember, there is no need to test for invalid inputs, the example is just for clarification.
Support different delimiters

To change a delimiter, the beginning of the string will contain a separate line that looks like "//[delimiter]\n[numbers…]". For example, "//;\n1;2" returns 3.

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

Add a public method to StringCalculator with signature
```
 int GetCalledCount()
```
The method returns the numer times Add was called.

Remember to start with a failing (or even noncompiling) test.
Add an event to the StringCalculator class
```
 public event Action<string, int> AddOccured
```
that is triggered after every Add call.

Hint: Create the event declaration first, then write a failing test that listens to the event and proves it should have been triggered when calling Add.

Hint 2: Example:
```
 string giveninput = null;
 sc.AddOccured += delegate(string input, int result)
 {
     giveninput = input;
 };
```
Numbers bigger than 1000 should be ignored, so adding 2 and 1001 returns 2.
Delimiters can be of any length with the following format: "//[delimiter]\n". For example "//[***]\n1***2***3" returns 6.
Allow multiple delimiters like this: "//[delim1][delim2]\n". For example "//[*][%]\n1*2%3" returns 6.
Make sure you can also handle multiple delimiters with length longer than one char.

ralphhendriks/string-calculator-kata

String Calculator Kata

Instructions

Steps