Test modules in PyTest

Introduction

Test modules help organize your tests in separate files. This makes testing easier and keeps your code clean.

When you want to group related tests together in one file.

When your project grows and you need multiple test files.

When you want to run tests from a specific file only.

When you want to share setup code across tests in one module.

When you want to keep tests separate from your main code.

Syntax

PyTest

Create a Python file starting with test_ or ending with _test.py
Inside, write test functions starting with test_
Example:

def test_example():
    assert 1 + 1 == 2

Test modules must be named so pytest can find them automatically.

Test functions inside modules must start with test_ to be recognized.

Examples

This module tests addition. The function name starts with test_.

PyTest

# File: test_math.py

def test_addition():
    assert 2 + 3 == 5

This module ends with _test.py and contains a subtraction test.

PyTest

# File: calculator_test.py

def test_subtraction():
    assert 5 - 2 == 3

Sample Program

This test module has three simple tests for string methods. Each test checks a different behavior.

PyTest

# File: test_sample.py

def test_uppercase():
    word = "hello"
    assert word.upper() == "HELLO"

def test_isupper():
    word = "HELLO"
    assert word.isupper() is True

def test_split():
    sentence = "hello world"
    assert sentence.split() == ["hello", "world"]

Important Notes

Always name your test files and functions properly so pytest can find and run them.

You can run tests from one module by specifying the file name: pytest test_sample.py.

Keep tests small and focused inside each module for easier debugging.

Summary

Test modules are Python files named to be found by pytest.

They group related tests for better organization.

Test functions inside must start with test_ to run automatically.