📟 String Calculator - TDD Kata (Java)

A clean and well-tested Java implementation of the String Calculator Kata, built using the principles of Test-Driven Development (TDD).
This project is part of the Incubyte Software Craftsmanship Assessment and demonstrates commitment to quality, clarity, and robust handling of inputs.

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✅ Features Implemented

Step	Feature Description
1.1	Return 0 for empty string
1.2	Return number itself for single input
1.3	Support comma-separated numbers
2	Support any number of values
3	Allow newline (\n) as a delimiter
4	Support custom single-character delimiters via header (e.g., //;\n1;2)
5-6	Throw exception for negative numbers and list all in the message
7	getCalledCount() method returns number of times add() was called
9	Ignore numbers greater than 1000
10	Support custom delimiters of any length (e.g., //[***]\n1***2***3)
11	Support multiple single-character delimiters (e.g., //[*][%]\n1*2%3)
12	Support multiple multi-character delimiters (e.g., //[**][%%]\n1**2%%3)

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❌ Strict Delimiter Format Enforced

This implementation strictly follows the TDD Kata specification:

• Multi-character delimiters must be enclosed in square brackets ([ ])
• Example:
  • ✅ Valid: //[***]\n1***2***3
  • ❌ Invalid: //***\n1***2***3 → throws IllegalArgumentException

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🧪 Test Suite (JUnit 5)

The project includes a comprehensive set of positive and negative test cases using JUnit 5, all located in: src/test/java/com/incubyte/StringCalculatorTest.java

✔️ Positive Test Highlights:

• Handles empty, single, and multiple values
• Supports various delimiters (,, \n, custom ones)
• Ignores numbers over 1000
• Tracks how many times add() was invoked

❌ Negative Test Highlights:

• Rejects unbracketed multi-character delimiters
• Throws on negative numbers with detailed messages
• Fails on non-numeric inputs
• Throws exception for null inputs

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🧠 Design Principles

• 🔁 TDD-first: every feature is written test-first
• 🧼 Clean, readable Java code
• 🧪 Well-separated test cases for clarity
• 🔒 Strict validation rules to match problem spec

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🧰 Tech Stack

• Java 17+
• JUnit 5
• IntelliJ IDEA (recommended)
• Git (with step-by-step commits)

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📂 Project Structure

src/
├── main/
│ └── java/com/incubyte/
│ └── StringCalculator.java # Business logic
├── test/
│ └── java/com/incubyte/
│ └── StringCalculatorTest.java # JUnit test suite

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▶️ How to Run Tests (in IntelliJ)

1. Right-click StringCalculatorTest class.
2. Select Run 'StringCalculatorTest'.
3. View results in the output/test panel.

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💡 Sample Usage

StringCalculator calc = new StringCalculator();
int result = calc.add("1,2\n3"); // returns 6
int count = calc.getCalledCount(); // returns 1

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📎 References

• TDD Kata blog by Incubyte
• TDD Kata by Roy Osherove

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Crafted and Maintained with ❤️ by Jeet Bhuptani