Run Nx integration tests sequentially to prevent shared-sandbox race condition

[thebraziliandeveloper]

Problem

When Nx runs multiple affected projects in parallel (default --parallel=3), each project's PHPUnit bootstrap runs concurrently inside the same Warden php-fpm container, sharing the same bind-mounted filesystem. This produces two classes of race condition that crash the integration test bootstrap before any tests execute:

1. deployTestModules.php conflicts

Both bootstraps call deployTestModules.php simultaneously. Each process removes and re-copies to app/code/Magento/TestModule*/ at the same time — one process deletes directories the other just created, or two mkdir() calls collide on the same path, triggering a "File exists" PHP warning that the integration test error handler converts into a fatal PHPUnit\Framework\Exception.

2. Shared sandbox directory conflict

Both bootstraps call setup:install via Magento\TestFramework\Application::install(), which creates a sandbox directory under:

dev/tests/integration/tmp/sandbox-0-<sha256(sha1(install-config))>/

Because both targets share the same phpunit.xml.dist and install-config-mysql.php, they compute an identical sandbox path. The second process to call mkdir() on that path fails with "File exists", again converted to a fatal bootstrap exception.

Fix

Add --parallel=1 to the nx affected command so test targets execute sequentially:

-nx affected --target=test:integration --head=HEAD --base=remotes/origin/${{ inputs.pr_base }}
+nx affected --target=test:integration --head=HEAD --base=remotes/origin/${{ inputs.pr_base }} --parallel=1

Trade-off

Sequential execution increases wall-clock time when multiple packages are affected simultaneously. However:

• Most PRs touch 1–2 packages, so the practical impact is small.
• The Warden stack (DB, Redis, RabbitMQ, OpenSearch) is a shared resource anyway, so true parallelism offers limited speed benefit.
• The tests were failing entirely without this change — reliability over speed.

A longer-term fix would give each test target a distinct install config (different DB name), producing unique sandbox paths and eliminating the shared-state problem while restoring parallelism.

Related

Follows #379 (cache key fix, already merged).

🤖 Generated with Claude Code

[rhoerr]

Thank you. Seems plausible and safe. Merging to try it on mage-os/mageos-magento2#213 .