Unit Testing in Python using UnitTest Framework

simple_calculator.py

#!/usr/bin/env python3


class SimpleCalculator:
    def sum(self, a, b):
        """ Function to add two integers """
        if isinstance(a, int) and isinstance(b, int):
            return a + b
        else:
            return "ERROR"

    def subtract(self, a, b):
        if isinstance(a, int) and isinstance(b, int):
            return a - b
        else:
            return "ERROR"

    def multiply(self, a, b):
        if isinstance(a, int) and isinstance(b, int):
            return a * b
        else:
            return "ERROR"

    def divide(self, a, b):
        if isinstance(a, int) and isinstance(b, int):
            return a / b
        elif b == 0:
            raise ZeroDivisionError("Cannot divide by zero")
        else:
            return "ERROR"

test_simple_calculator.py

#!/usr/bin/env python3
import unittest
from simple_calculator import SimpleCalculator


class AdditionTestSuite(unittest.TestCase):
    def setUp(self):
        """ Executed before every test case """
        self.calculator = SimpleCalculator()

    def test_addition_two_integers(self):
        result = self.calculator.sum(5, 6)
        self.assertEqual(result, 11)

    def test_addition_integer_string(self):
        result = self.calculator.sum(5, "6")
        self.assertEqual(result, "ERROR")

    def test_addition_negative_integers(self):
        result = self.calculator.sum(-5, -6)
        self.assertEqual(result, -11)
        self.assertNotEqual(result, 11)


class SubtractionTestSuite(unittest.TestCase):
    def setUp(self):
        """ Executed before every test case """
        self.calculator = SimpleCalculator()

    def test_substration_two_integers(self):
        result = self.calculator.subtract(6, 5)
        self.assertEqual(result, 1)

    def test_subtraction_integer_string(self):
        result = self.calculator.subtract(5, "6")
        self.assertEqual(result, "ERROR")

    def test_subtraction_negative_integers(self):
        result = self.calculator.subtract(-5, -6)
        self.assertEqual(result, 1)
        self.assertNotEqual(result, -11)        


class MultiplicationTestSuite(unittest.TestCase):
    def setUp(self):
        """ Executed before every test case """
        self.calculator = SimpleCalculator()

    def test_multiplication_two_integers(self):
        result = self.calculator.multiply(6, 5)
        self.assertEqual(result, 30)

    def test_multiplication_integer_string(self):
        result = self.calculator.subtract(5, "6")
        self.assertEqual(result, "ERROR")

    def test_multiplication_negative_integers(self):
        result = self.calculator.multiply(-5, -6)
        self.assertEqual(result, 30)
        self.assertNotEqual(result, -30)         


class DivisionTestSuite(unittest.TestCase):
    def setUp(self):
        """ Executed before every test case """
        self.calculator = SimpleCalculator()

    def test_division_two_integers(self):
        result = self.calculator.divide(30, 5)
        self.assertEqual(result, 6)

    def test_division_integer_string(self):
        result = self.calculator.divide(5, "6")
        self.assertEqual(result, "ERROR")

    def test_division_negative_integers(self):
        result = self.calculator.divide(-30, -6)
        self.assertEqual(result, 5)
        self.assertNotEqual(result, -5)  

    def test_divide_by_zero_exception(self):
        with self.assertRaises(ZeroDivisionError):
            self.calculator.divide(10, 0)


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