pytest-xdist for parallel execution

Introduction

Running tests one by one can take a long time. pytest-xdist helps run tests at the same time to save time.

You have many tests and want to finish them faster.

You want to use all your computer's CPU cores to run tests.

You want to run tests in parallel on different machines.

You want to reduce waiting time before seeing test results.

Syntax

PyTest

pytest -n <num_workers>

-n option tells pytest how many workers to use to run tests in parallel.

You can use auto to use all CPU cores automatically.

Examples

Run tests using 4 workers in parallel.

PyTest

pytest -n 4

Run tests using all available CPU cores automatically.

PyTest

pytest -n auto

Sample Program

This example has 4 tests that each wait 1 second. Running with -n 4 runs all at the same time, so total time is about 1 second instead of 4.

PyTest

import time

def test_one():
    time.sleep(1)
    assert True

def test_two():
    time.sleep(1)
    assert True

def test_three():
    time.sleep(1)
    assert True

def test_four():
    time.sleep(1)
    assert True

# Run this command in terminal:
# pytest -n 4

Important Notes

Make sure your tests do not share or change the same data when running in parallel.

pytest-xdist must be installed with pip install pytest-xdist.

Some tests that depend on order or shared resources may fail when run in parallel.

Summary

pytest-xdist runs tests at the same time to save time.

Use pytest -n <num> to set how many tests run in parallel.

Good for speeding up large test suites on multi-core computers.