Meeting the Unittest

Introduction to Testing in Python

Alexander Levin

Data Scientist

Recap of OOP

OOP - programming paradigm based on objects and classes.
Class - a template of an object that can contain methods and attributes.
Method - a function or procedure that belongs to a class.
Attribute - a variable that belongs to a class.
Object - an instance of a class.

Example of a Python class:

class Rectangle:
  # Constructor of Rectangle
  def __init__(self, a, b):
      self.a = a
      self.b = b
  # Area method
  def get_area(self):
      return self.a * self.b
# Usage example
r = Rectangle(4, 5)
print(r.get_area())

>> 20

OOP Inheritance

Classes can inherit properties from other classes.
Put the parent class in the brackets after the name of the new class.
```
class RedRectangle(Rectangle):
  self.color = 'red'
```

What is unittest

unittest - built-in Python framework for test automation (it is installed with Python).
unittest - not only for unit tests alone.
Based on OOP: each test case is a class, and each test is a method.
Test case - is an instance of testing.
Test suite - is a collection of test cases.

unittest vs. pytest

unittest

OOP-based - requires to create test classes)
Built-in (is installed with the Python distribution)
More assertion methods

pytest

Functon-based - searches for scripts and functions starting with test_
Third-party package (has to be installed separately from the Python distribution)
Less assertion methods

How to create a test with unittest

Test of the exponentiation operator:

import unittest

# Declaring the TestCase class
class TestSquared(unittest.TestCase):
    # Defining the test
    def test_negative(self):
        self.assertEqual((-3) ** 2, 9)

Assertion methods

.assertEqual(), .assertNotEqual()
.assertTrue(), .assertFalse()
.assertIs(), .assertIsNone()
.assertIsInstance(), .assertIn()
.assertRaises()
Many others

Summary

unittest - OOP-based built-in Python framework for test automation
Test case - is a testing instance in unittest
To create a test:
1. Declare a class inheriting from unittest.TestCase
2. Define test functions
Assertion methods

Let's practice!

Introduction to Testing in Python