Test functions in PyTest

Introduction

Test functions help check if parts of your code work correctly. They make sure your program does what you expect.

When you want to check if a function returns the right result.

When you fix a bug and want to confirm it is really fixed.

When you add new features and want to make sure old parts still work.

When you want to run quick checks automatically without manual testing.

Syntax

PyTest

def test_function_name():
    assert expression

Test functions start with test_ so pytest can find them.

Use assert to check if something is true.

Examples

This test checks if 2 plus 2 equals 4.

PyTest

def test_addition():
    assert 2 + 2 == 4

This test checks if the length of 'hello' is 5.

PyTest

def test_string_length():
    assert len('hello') == 5

This test checks if the number 3 is in the list.

PyTest

def test_list_contains():
    assert 3 in [1, 2, 3]

Sample Program

This program defines a simple add function and tests it with three cases. Each assert checks if the result is correct.

PyTest

def add(a, b):
    return a + b

def test_add():
    assert add(3, 4) == 7
    assert add(-1, 1) == 0
    assert add(0, 0) == 0

Important Notes

Keep test functions small and focused on one thing.

Use clear names starting with test_ so pytest finds them easily.

Run tests often to catch problems early.

Summary

Test functions check if code works as expected.

They start with test_ and use assert statements.

Running tests helps keep your code reliable and bug-free.