String Calculator TDD Kata

A production-grade implementation of the famous String Calculator Kata, demonstrating strict Test-Driven Development (TDD) practices and clean architecture principles.

🚀 Features

This calculator handles complex string parsing scenarios including:

• Basic Arithmetic: Sums comma-separated integers.
• Robust Parsing: Handles newlines (\n) and custom delimiters seamlessly.
• Advanced Delimiters:
  • Custom single-character delimiters (e.g., //;\n1;2)
  • Multi-character delimiters (e.g., //[***]\n1***2***3)
  • Multiple different delimiters (e.g., //[*][%]\n1*2%3)
  • Multiple multi-character delimiters (e.g., //[foo][bar]\n1foo2bar3)
• Safety:
  • Ignores empty entries caused by consecutive delimiters (1,,2 → 3).
  • Ignores numbers > 1000.
  • Throws informative exceptions for negative numbers, listing all offenders.

#	Feature	Example	Output	Status
1	Empty String	add("")	0	✅
2	Single Number	add("1")	1	✅
3	Multiple Numbers	add("1,2,3")	6	✅
4	Newline Delimiter	add("1\n2,3")	6	✅
5	Custom Delimiter	add("//;\n1;2")	3	✅
6	Negative Exception	add("-1,2")	Exception	✅
7	All Negatives Listed	add("-1,-2")	Exception: -1, -2	✅
8	Ignore > 1000	add("2,1001")	2	✅
9	Multi-char Delimiter	add("//[***]\n1***2")	3	✅
10	Multiple Delimiters	add("//[*][%]\n1*2%3")	6	✅
11	Multi-char Multiple	add("//[foo][bar]\n1foo2bar3")	6	✅
12	Consecutive Delimiters	add("1,,2")	3	✅
13	Trailing Delimiters	add("1,2,")	3	✅
14	Boundary (1000)	add("1000,1001,5")	1005	✅
15	Invalid Input	add("1,a,3")	Exception	✅

🛠️ Technical Approach

This project was built using the Red-Green-Refactor cycle.

Key Design Decisions

1. Unified Regex Parsing: Instead of messy if-else chains for different delimiter types, the solution compiles all delimiters into a single RegExp. This makes the add method purely functional and declarative.
2. Immutability: The code prioritizes final variables and pure functions to reduce side effects.
3. Defensive Coding:
   • RegExp.escape() is used to prevent special characters (like * or +) from crashing the parser.
   • Boundary checks (e.g., inclusive vs exclusive limits) are explicitly tested.

🧪 Running Tests

This project uses the standard test package.

Run all tests:

dart test

Run with expanded output (to see individual test cases):

dart test -r expanded

✅ Test Results

📂 Project Structure

string_calculator_kata/
├── lib/
│   ├── string_calculator_kata.dart  # Main logic (Parse -> Filter -> Reduce)
└── test/
│   └── string_calculator_kata_test.dart  # Comprehensive test suite
└── README.md

📝 Commit History

The git log of this repository serves as proof of the TDD process, featuring atomic commits tagged with test: [RED], feat: [GREEN], and refactor steps.

Implemented as part of the Incubyte TDD Assessment.