Parallel execution in CI in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is parallel execution in Continuous Integration (CI)?

Parallel execution in CI means running multiple tests at the same time to save time and get faster feedback on code changes.

beginner

How does pytest support parallel test execution?

Pytest supports parallel test execution using the plugin called pytest-xdist, which allows tests to run on multiple CPU cores simultaneously.

beginner

What is a common command to run pytest tests in parallel using 4 CPUs?

The command is pytest -n 4, where -n 4 tells pytest to use 4 CPU cores for running tests in parallel.

beginner

Why is parallel execution useful in CI pipelines?

It reduces the total test run time, helping developers get quick feedback and merge code faster, improving productivity and code quality.

intermediate

Name one challenge when running tests in parallel in CI.

Tests might interfere with each other if they share resources like files or databases, causing flaky or failing tests.

Which pytest plugin enables parallel test execution?

A pytest-cov

B pytest-mock

C pytest-html

D pytest-xdist

The pytest-xdist plugin allows tests to run in parallel across multiple CPUs.

What does the command pytest -n 3 do?

A Runs tests sequentially 3 times

B Runs tests on 3 CPU cores in parallel

C Runs only 3 tests

D Runs tests with 3 retries

The -n 3 option tells pytest to run tests in parallel using 3 CPU cores.

Why might tests fail when run in parallel in CI?

A Because tests share resources causing conflicts

B Because tests run too slowly

C Because pytest does not support parallelism

D Because CI servers do not allow parallel jobs

Tests sharing resources like files or databases can interfere with each other when run in parallel.

What is a key benefit of parallel test execution in CI?

A Slower test runs

B More manual testing

C Faster feedback on code changes

D Less test coverage

Parallel execution speeds up tests, giving developers faster feedback.

Which of these is NOT a good practice for parallel tests?

A Sharing global state between tests

B Isolating test data

C Using separate test databases

D Avoiding file conflicts

Sharing global state can cause tests to interfere and fail when run in parallel.

Explain how pytest can run tests in parallel in a CI environment and why this is helpful.

Think about how multiple tests can run at the same time to save time.

Describe one challenge you might face when running tests in parallel and how to avoid it.

Consider what happens if two tests try to change the same file at once.