Introduction to testing in Python

Introduction to Testing in Python

Alexander Levin

Data Scientist

Why is testing so important?

Common problems:

Bugs and errors
Hardware failures
Unexpected or unpredictable behavior

All of the problems might lead to significant expenses increase for the fixing purposes.

Testing helps to:

Identify defects, bugs, and errors
Reduce risks of software failures
Enhance reliability, functionality, and performance of the software

What is testing?

Testing - a process of evaluating a system or software
We need testing to ensure it meets specified requirements
Test - a procedure to verify the correctness of a software application or system

Course prerequisites

Advanced Python programming
assert statements
Decorators
OOP Concepts (classes, methods, inheritance)

Testing in real life

Think of airplanes:

Visual inspection
Electronics and mechanics check
Fuel check
Passengers check
Weather check
Permission to take off from air traffic controller

All of the above - are tests! And we need them for safety.

airplane before take-off

Assert in Python

assert condition - lets to test if condition is True.
If condition is False, Python will raise an AssertionError.

Testing with pytest - a simple example

pytest - a popular testing framework in Python, which provides a simple way to write tests.

Example of an "assert" test written with pytest in Python:

import pytest

# A function to test
def squared(number):
    return number * number

# A test function always starts with "test"
def test_squared():
    assert squared(-2) == squared(2)

Context managers recap

Context manager - a Python object that is used by declaring a with statement
We use context managers to set up and tear down temporary context

# Writing to file example
with open("hello_world.txt", 'w') as hello_file:
    hello_file.write("Hello world \n")

Meet the pytest: raises

pytest.raises - when you expect the test to raise an Exception

import pytest

# A function to test
def division(a, b):
    return a / b

# A test function
def test_raises():
    with pytest.raises(ZeroDivisionError):
        division(a=25, b=0)

Summary

Testing is:

A process of evaluating, that software works as expected
Present in everyday life
Essential to tackle the challenges of the software development process
Helps to ensure that the problems are addressed properly

Tests implementation:

pytest - a powerful Python framework, that simplifies the testing process
assert - a Python keyword, used in pytest for creating basic tests by validating a condition
pytest.raises- a context manager, used to create a test that is expected to result in Exception

Let's practice!

Introduction to Testing in Python