Why parametrize multiplies test coverage in PyTest - Test Execution Impact

Test Overview

This test uses pytest's parametrize feature to run the same test logic with different inputs. It verifies that the function correctly identifies even numbers for multiple cases, increasing test coverage efficiently.

Test Code - pytest

PyTest

import pytest

def is_even(num):
    return num % 2 == 0

@pytest.mark.parametrize("input_num,expected", [
    (2, True),
    (3, False),
    (0, True),
    (-4, True),
    (7, False)
])
def test_is_even(input_num, expected):
    assert is_even(input_num) == expected

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts with input_num=2 and expected=True	Test environment ready, function is_even loaded	Check if is_even(2) == True	PASS
2	Test runs with input_num=3 and expected=False	Same test function reused with new parameters	Check if is_even(3) == False	PASS
3	Test runs with input_num=0 and expected=True	Test function called again with zero input	Check if is_even(0) == True	PASS
4	Test runs with input_num=-4 and expected=True	Negative even number tested	Check if is_even(-4) == True	PASS
5	Test runs with input_num=7 and expected=False	Odd number tested last	Check if is_even(7) == False	PASS

Failure Scenario

Failing Condition: If is_even returns wrong result for any input

Execution Trace Quiz - 3 Questions

What does pytest parametrize do in this test?

A Skips tests that fail

B Runs different test functions automatically

C Runs the same test multiple times with different inputs

D Runs tests only once

Key Result

Using parametrize in pytest lets you run one test with many inputs, multiplying coverage without writing many test functions.