Running with -n auto in PyTest - Test Execution Trace

Test Overview

This test runs multiple test functions in parallel using pytest with the -n auto option. It verifies that all tests execute and pass concurrently, speeding up the test suite.

Test Code - pytest

PyTest

import pytest

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

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

def test_multiplication():
    assert 3 * 4 == 12

if __name__ == "__main__":
    pytest.main(["-n", "auto"])

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts with pytest and option '-n auto' to enable parallel execution	pytest initializes and detects 3 test functions in the file	-	PASS
2	pytest-xdist plugin creates worker processes equal to CPU cores available	Multiple worker processes ready to run tests in parallel	-	PASS
3	Each worker process runs one or more test functions concurrently	test_addition, test_subtraction, and test_multiplication executing in parallel	-	PASS
4	Assertions inside each test function are checked	Each test function completes and returns pass if assertion is true	assert 1 + 1 == 2, assert 5 - 3 == 2, assert 3 * 4 == 12	PASS
5	pytest collects results from all workers and aggregates the test report	All tests passed, report shows 3 passed tests	All tests passed without errors	PASS

Failure Scenario

Failing Condition: One or more test assertions fail during parallel execution

Execution Trace Quiz - 3 Questions

What does the '-n auto' option do when running pytest?

A Runs tests sequentially in a single process

B Runs tests in parallel using all CPU cores

C Skips tests marked as slow

D Runs tests only on a single CPU core

Key Result

Using '-n auto' with pytest-xdist runs tests in parallel across CPU cores, which speeds up testing but requires tests to be independent and free of shared state to avoid flaky failures.