Python 3 unit test

Question

1st: I want to write a function "div" that takes two numbers as parameters and returns the quotient of the first number divided by the second number. and need to use a try-except statement to do the division. And in case of division by 0, use the except clause to return a special float value 'nan' (not a number).

2nd: After that, I need to design a number of test cases to test the function (unit test) with the aim of identifying all possible errors of the function. For each test, specify both the input and the expected output. For each test case, carry out the test and compare the actual test result with the expected result..

I'm did 1st point-

def div(a, b):
    try:
        return a / b
    except ZeroDivisionError:
        return float('nan')

I'm stuck on the 2nd point called "unit testing"

Can someone please help me?

Answer 1

how about:

class TestDivFunction(unittest.TestCase):

    def test_division(self):
        self.assertEqual(div(10, 2), 5)
        self.assertEqual(div(-10, 2), -5)
        self.assertEqual(div(0, 1), 0)

    def test_division_by_zero(self):
        self.assertTrue(math.isnan(div(10, 0)))

Answer 2

I think that your function div is perfect to answer to your 1st point. I suppose that your function is saved in a file called div_function.py. So the content of the file div_function.py is exactly your code:

def div(a, b):
    try:
        return a / b
    except ZeroDivisionError:
        return float('nan')

For the 2nd point you can use the Python unittest module and create some tests function which will validate your code. An example of a file able to execute these tests is the following:

import math
import unittest
from div_function import div

class TestDiv(unittest.TestCase):

    # test 1: 20:2 == 10
    def test_div_01(self):
        self.assertEqual(10, div(20, 2))

    # test 2: 11:2 == 5.5
    def test_div_02(self):
        self.assertEqual(5.5, div(11, 2))

    # test 3: 10:3 (with 3 decimal) == 3.333
    def test_div_03(self):
        self.assertEqual(3.333, round(div(10, 3),3))

    # test of 'nan': 10:0 is not possible
    def test_div_04(self):
        self.assertTrue(math.isnan(div(10, 0)))

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

See the comments added to every tests for some other details.