This document outlines a string calculator kata following the Open-Closed Principle (OCP) design rules. It provides test cases for basic integer arithmetic operations like addition, subtraction, multiplication, and division expressed as strings. Additional challenges are given for expressions containing multiple operations that require proper order of operations to evaluate correctly. The goal is to write a calculator class that can evaluate these string expressions as integers based on the given tests.

1. OCP String Calculator Kata
Using the OCP rules, write a very simple
string calculator using the following test template:
public class CalculatorTester {
@Test
public void sampleTest() {
Calculator calculator = new CalculatorFactory().create();
assertEquals(4, calculator.evaluate("2 + 2"));
}
}

2. OCP String Calculator Kata
The tests are:
" " -> 0
"234" -> 234
"6 + 3" -> 9
"12 + 34" -> 46
"6 - 3" -> 3
"18 - 4" -> 14
"6 * 3" -> 18
"5 * 22" -> 110
"6 / 3" -> 2
"36 / 12" -> 3
You can assume that:

A single space char separates the operator from the numbers.

Only integer arithmetic is to be supported.

3. OCP String Calculator Kata
Additional challenges:
"18 - 4 + 3" -> 17
"18 - 4 * 3" -> 6
"18 - (4 + 3)" -> 11
Only integer arithmetic is to be supported.