Branch coverage in PyTest

Introduction

Branch coverage helps us check if every decision point in our code has been tested. It makes sure all possible paths are tried.

When you want to test all if-else conditions in your code.

When you want to find untested parts in decision-making code.

When you want to improve test quality by covering all branches.

When you want to avoid bugs hidden in rarely used code paths.

Syntax

PyTest

pytest --cov=your_module --cov-branch

This command runs tests and measures branch coverage.

Use --cov-branch to include branch coverage, not just line coverage.

Examples

Run tests on myapp and check branch coverage.

PyTest

pytest --cov=myapp --cov-branch

Run tests on calculator with branch coverage and verbose output.

PyTest

pytest --cov=calculator --cov-branch -v

Sample Program

This simple function returns the bigger of two numbers. The test checks both branches: when a is greater and when b is greater.

PyTest

def max_value(a, b):
    if a > b:
        return a
    else:
        return b


def test_max_value():
    assert max_value(5, 3) == 5
    assert max_value(2, 4) == 4

# Run with: pytest --cov=sample_module --cov-branch

Important Notes

Branch coverage is stricter than line coverage because it checks all decision outcomes.

Use branch coverage to find missing tests in if-else and switch cases.

High branch coverage means your tests explore all logical paths.

Summary

Branch coverage tests all possible paths in decision points.

Use pytest --cov --cov-branch to measure it.

It helps find untested branches and improve test quality.