tests: xdist

[mscolnick]

This pull request introduces parallel test execution using pytest-xdist across the codebase, improves test reliability with a new fixture, and makes minor improvements to code consistency and determinism. The key changes are grouped below.

Test Parallelization and Workflow Updates:

• Added pytest-xdist as a test dependency in pyproject.toml to enable parallel test execution.
• Updated test commands in GitHub Actions workflows (test_be.yaml, test_cli.yaml) to use the -n auto flag, enabling parallel test runs for improved CI speed. [1] [2] [3] [4]
• Increased the build job timeout in dev_build.yaml to 20 minutes to accommodate potentially longer parallel builds.

Test Reliability and Infrastructure:

• Added an autouse pytest fixture in tests/conftest.py to ensure __main__.__file__ is set for each worker, preventing failures in tests that rely on this attribute when running with pytest-xdist.

Code Consistency and Determinism:

• Sorted the order of attributes when dynamically creating test classes in marimo/_ast/pytest.py for consistent test behavior.
• Ensured deterministic ordering of collected functions in tests/_runtime/test_complete.py by sorting them by module and qualified name.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Mar 27, 2026 5:05pm

[Copilot]

Pull request overview

This PR enables running the Python test suite under pytest-xdist (parallel execution) and adds a few determinism fixes to avoid order-dependent failures when tests run concurrently.

Changes:

• Add pytest-xdist to the test dependency group and enable -n auto in CI workflows.
• Add a global test fixture intended to ensure __main__.__file__ is set in xdist workers.
• Make ordering deterministic in a runtime completion test and in marimo’s pytest AST test-class generation.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/conftest.py	Adds an autouse fixture to patch __main__.__file__ for xdist workers.
tests/_runtime/test_complete.py	Sorts collected callables for deterministic parametrization order.
pyproject.toml	Adds pytest-xdist to the test dependency group.
marimo/_ast/pytest.py	Sorts defs to make generated pytest class attributes deterministic.
.github/workflows/test_cli.yaml	Runs CLI tests with pytest -n auto.
.github/workflows/test_be.yaml	Runs backend tests with pytest -n auto across dependency matrices.
.github/workflows/dev_build.yaml	Adds a job timeout limit.

[akshayka]

Nice. Can you leave a comment documenting the issue on Windows, with a TODO to fix it?

These are the tests I saw that failed.

FAILED tests/_islands/test_island_generator.py::test_build - worker 'gw1' crashed while running 'tests/_islands/test_island_generator.py::test_build'
FAILED tests/_messaging/test_streams.py::test_import_multiprocessing - worker 'gw0' crashed while running 'tests/_messaging/test_streams.py::test_import_multiprocessing'
FAILED tests/_server/api/endpoints/test_ai.py::TestOpenAiEndpoints::test_completion_without_token - worker 'gw2' crashed while running 'tests/_server/api/endpoints/test_ai.py::TestOpenAiEndpoints::test_completion_without_token'
FAILED tests/_server/test_session_manager.py::test_create_session_new - worker 'gw4' crashed while running 'tests/_server/test_session_manager.py::test_create_session_new'
FAILED tests/_islands/test_island_generator.py::test_render - worker 'gw5' crashed while running 'tests/_islands/test_island_generator.py::test_render'
FAILED tests/_server/test_session_manager.py::test_create_session_absolute_url - worker 'gw6' crashed while running 'tests/_server/test_session_manager.py::test_create_session_absolute_url'
FAILED tests/_islands/test_island_generator.py::test_render_multiline_markdown - worker 'gw7' crashed while running 'tests/_islands/test_island_generator.py::test_render_multiline_markdown'
FAILED tests/_server/test_session_manager.py::test_create_session_with_script_config_overrides - worker 'gw8' crashed while running 'tests/_server/test_session_manager.py::test_create_session_with_script_config_overrides'
FAILED tests/_server/test_session_manager.py::test_recents_touch_called_on_session_create - worker 'gw9' crashed while running 'tests/_server/test_session_manager.py::test_recents_touch_called_on_session_create'