Parallel execution in CI in PyTest - Test Execution Trace

Test Overview

This test runs multiple simple tests in parallel using pytest-xdist in a Continuous Integration (CI) environment. It verifies that tests execute concurrently and all pass successfully.

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

def test_division():
    assert 10 / 2 == 5

# To run in parallel in CI, use: pytest -n 4

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts with pytest and xdist plugin using '-n 4' to run 4 tests in parallel	CI environment initializes pytest with parallel workers	-	PASS
2	pytest discovers 4 test functions: test_addition, test_subtraction, test_multiplication, test_division	Test functions are ready to be executed concurrently	-	PASS
3	Each test runs in parallel worker process: test_addition runs and asserts 1 + 1 == 2	test_addition executes in worker 1	assert 1 + 1 == 2	PASS
4	test_subtraction runs in parallel worker process and asserts 5 - 3 == 2	test_subtraction executes in worker 2	assert 5 - 3 == 2	PASS
5	test_multiplication runs in parallel worker process and asserts 3 * 4 == 12	test_multiplication executes in worker 3	assert 3 * 4 == 12	PASS
6	test_division runs in parallel worker process and asserts 10 / 2 == 5	test_division executes in worker 4	assert 10 / 2 == 5	PASS
7	pytest collects results from all parallel workers and aggregates test report	CI system receives all test results	All tests passed	PASS

Failure Scenario

Failing Condition: One or more tests fail due to incorrect assertion or test error

Execution Trace Quiz - 3 Questions

What does the '-n 4' option do when running pytest in CI?

A Runs 4 tests in parallel using separate worker processes

B Runs tests sequentially 4 times

C Limits the test run to 4 tests total

D Skips 4 tests during execution

Key Result

Running tests in parallel in CI speeds up feedback but requires tests to be independent and free of shared state to avoid flaky failures.