Test Driven Development

Definition:

Test Driven Development (TDD) is a software development methodology where you write tests before writing the actual code. It follows a simple cycle: Red → Green → Refactor. TDD Cycle:

• Red: Write a failing test
• Green: Write minimal code to make the test pass
• Refactor: Improve the code while keeping tests passing

Example:

Calculator Addition Function Step 1: Red - Write Failing Test

import unittest

class TestCalculator(unittest.TestCase):
    def test_add_two_numbers(self):
        calc = Calculator()
        result = calc.add(2, 3)
        self.assertEqual(result, 5)

    def test_add_negative_numbers(self):
        calc = Calculator()
        result = calc.add(-1, -2)
        self.assertEqual(result, -3)

if __name__ == '__main__':
    unittest.main()

Step 2: Green - Write Minimal Code

class Calculator:
    def add(self, a, b):
        return a + b

Step 3: Refactor - Improve Code

class Calculator:
    def add(self, a: int, b: int) -> int:
        """Add two numbers and return the result."""
        if not isinstance(a, (int, float)) or not isinstance(b, (int, float)):
            raise TypeError("Both arguments must be numbers")
        return a + b

reference: Link-1