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Unit testing in Python

  • Python has a built-in module called unittest that you can use to write unit tests for your programs.
  • You can use this module to write tests for your own functions and make sure your code is working as expected.
  • Unit tests are some pieces of code to exercise the input, the output and the behaviour of your code.

Testing Classes

  • To test a class, we need to create a class that inherits from unittest.TestCase.
  • We use the setUp() method to create instances of the class we want to test.
  • We use the assertEqual() method to verify that the result obtained is the same as the expected result.
import unittest

def add(x, y):
    return x + y

class TestAdd(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(10, 20), 30)
        self.assertEqual(add(-10, 20), 10)
        self.assertEqual(add(-10, -20), -30)
        self.assertEqual(add(0, 0), 0)

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

Testing functions

  • assert

    • is a method provided by the unittest module.

    • It tests whether the result obtained is the same as the expected result.

      import unittest

def main():
    test_add()

def add(x, y):
    return x + y

def test_add():
    assert add(10, 20) == 30
    assert add(-10, 20) == 10
    assert add(-10, -20) == -30
    assert add(0, 0) == 0

if __name__ == '__main__':
  main()

  • assertRaises

    • is a method provided by the unittest module.

    • It tests whether the function raises an exception when it is called with the given arguments.

      import unittest

def main():
    test_divide()
    test_divide_raises()

def divide(x, y):
    if y == 0:
        raise ValueError("Can not divide by zero!")
    return x / y

def test_divide():
    assert divide(10, 2) == 5
    assert divide(10, 5) == 2
    assert divide(10, 0) == 0

def test_divide_raises():
    with assertRaises(ValueError):
        divide(10, 0)

if __name__ == '__main__':
  main()

Handing Test Exceptions

  • AssertionError

    • is raised when an assert statement fails.
    • it gives us ability to provide a custom message to be displayed when the assertion fails.
import unittest

def main():
    test_divide()

def divide(x, y):
    if y == 0:
        raise ValueError("Can not divide by zero!")
    return x / y

def test_divide():
    try:
        divide(10, 0)
    except AssertionError:
        print("AssertionError: Can not divide by zero!")

if __name__ == '__main__':
  main()

pytest

// TODO: read this tutorial and add notes

It's a framework that makes building simple and scalable tests easy.

  • it will run all files of the form test_*.py or *_test.py in the current directory and its subdirectories.

  • it will run all functions and classes which have names that start with test_ prefixed.

  • Example:

    • Test file: test_add.py

      import pytest

def add(x, y):
    return x + y

def test_add():
    # testing logic

    • To run the tests, enter the following command in the terminal:

      pytest

  • It provide us with descriptive output pytest