Branch coverage in PyTest - Test Execution Trace

Test Overview

This test checks a simple function with an if-else branch. It verifies that both branches are tested to achieve full branch coverage.

Test Code - pytest

PyTest

def is_even(num):
    if num % 2 == 0:
        return True
    else:
        return False

import pytest

def test_is_even():
    assert is_even(4) == True
    assert is_even(5) == False

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Calls is_even(4)	Function receives input 4	Check if 4 % 2 == 0 branch is taken	PASS
3	Returns True for input 4	Function returns True	Assert returned value is True	PASS
4	Calls is_even(5)	Function receives input 5	Check if else branch is taken for 5	PASS
5	Returns False for input 5	Function returns False	Assert returned value is False	PASS
6	Test ends	All assertions passed	Branch coverage achieved for both if and else	PASS

Failure Scenario

Failing Condition: Only one branch of the if-else is tested, e.g., only is_even(4) is tested

Execution Trace Quiz - 3 Questions

What does branch coverage ensure in this test?

A Only the if branch is tested

B Only the else branch is tested

C Both the if and else branches are executed during testing

D No branches are tested

Key Result

To achieve full branch coverage, tests must include inputs that cause every branch of conditional statements to execute.