pytest-cov for coverage

Introduction

pytest-cov helps you see how much of your code is tested. It shows which parts are checked and which are not.

You want to check if your tests cover all important parts of your program.

Before sharing your code, to make sure tests are thorough.

When adding new features, to confirm tests cover them.

To find untested code that might cause bugs.

To improve test quality by focusing on uncovered code.

Syntax

PyTest

pytest --cov=your_package tests/

Replace your_package with the folder or module you want coverage for.

tests/ is the folder where your test files are located.

Examples

Runs tests in tests/ and measures coverage for the myapp package.

PyTest

pytest --cov=myapp tests/

Shows coverage report in the terminal and highlights missing lines.

PyTest

pytest --cov=myapp --cov-report=term-missing tests/

Generates an HTML report you can open in a browser to see coverage details.

PyTest

pytest --cov=myapp --cov-report=html tests/

Sample Program

This example has a simple module with two functions: add and subtract. The test only checks add. Running pytest with coverage will show subtract is not tested.

PyTest

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

def subtract(a, b):
    return a - b

# test_sample.py
import pytest
from sample import add

def test_add():
    assert add(2, 3) == 5

Important Notes

Install pytest-cov with pip install pytest-cov before using it.

Use --cov-report=term-missing to see exactly which lines are not covered.

HTML reports help visualize coverage in a friendly way.

Summary

pytest-cov shows how much of your code is tested.

Run tests with pytest --cov=your_package to get coverage info.

Use reports to find untested code and improve your tests.