pytest-xdist

# Assuming you have pytest and pytest-xdist installed and tests in a 'tests/' directory
# Create a simple test file, e.g., tests/test_example.py
# import time
# def test_fast():
#     assert True
# def test_medium():
#     time.sleep(0.5)
#     assert True
# def test_slow():
#     time.sleep(1)
#     assert True

import os
import subprocess

def run_pytest_xdist(num_processes):
    cmd = ['pytest', '-n', str(num_processes)]
    print(f"Running: {' '.join(cmd)}")
    result = subprocess.run(cmd, capture_output=True, text=True)
    print(result.stdout)
    if result.stderr:
        print("STDERR:", result.stderr)
    return result.returncode

# Example usage: run tests on all available CPU cores
# A real-world scenario would just be `pytest -n auto` from the command line
if __name__ == '__main__':
    # Ensure pytest is installed for this example to run locally in a script
    try:
        import pytest
    except ImportError:
        print("pytest is not installed. Please install with 'pip install pytest'.")
        exit(1)

    print("\n--- Running tests with pytest -n auto ---")
    # In a real shell, you would simply type: pytest -n auto
    # For programmatic execution, we demonstrate the subprocess call
    exit_code = run_pytest_xdist('auto')
    if exit_code == 0:
        print("Tests passed successfully with -n auto.")
    else:
        print(f"Tests failed with -n auto. Exit code: {exit_code}")

    print("\n--- Running tests with pytest -n 2 ---")
    # In a real shell, you would simply type: pytest -n 2
    exit_code = run_pytest_xdist(2)
    if exit_code == 0:
        print("Tests passed successfully with -n 2.")
    else:
        print(f"Tests failed with -n 2. Exit code: {exit_code}")