Add virtual display for XCUITests on headless Depot runners

[lawrencecchen]

Summary

• Depot macOS runners have no physical display. system_profiler SPDisplaysDataType returns empty, and XCUITests fail with Failed to activate application (current state: Running Background) because macOS can't bring the app to foreground without a display.
• Adds scripts/create-virtual-display.m, a small ObjC tool that creates a 1920x1080 virtual display using the private CGVirtualDisplay API (same approach used by Chromium CI). Runs as a background process during the workflow, dies when the step completes.
• Workflow compiles and launches the tool before tests, with before/after display diagnostics.

Testing

• Compiled and verified locally: clang -framework Foundation -framework CoreGraphics -o /tmp/create-virtual-display scripts/create-virtual-display.m && /tmp/create-virtual-display produces Virtual display created: 1920x1080@60Hz (displayID: 10)
• Merge to main, then trigger: gh workflow run test-depot.yml -f skip_unit_tests=true -f test_filter=UpdatePillUITests

Related

• Follow-up to PR Improve Depot test workflow: diagnostics, filter, timeout #720 (diagnostics showed empty display on Depot)

Summary by CodeRabbit

Release Notes

• Chores
  • Enhanced CI testing infrastructure with support for filtered test execution and customizable per-test timeouts.
  • Added virtual display support for headless testing environments, enabling UI tests to run reliably in CI/CD pipelines without a physical display.

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Mar 1, 2026 0:26am

[coderabbitai]

Note

Currently processing new changes in this PR. This may take a few minutes, please wait...

📥 Commits

Reviewing files that changed from the base of the PR and between 1b160dc and a0d58e2.

📒 Files selected for processing (2)

• .github/workflows/test-depot.yml
• scripts/create-virtual-display.m

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch task-xcuitests-depot

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[chatgpt-codex-connector]

Fail if virtual display process dies after launch

Starting the helper with /tmp/create-virtual-display & does not propagate its runtime failure to the step, so if CGVirtualDisplay is unavailable (or the helper exits for any reason), this step still succeeds and the workflow proceeds with no active display; UI tests then fail later with unrelated foreground-activation errors. Because set -e does not monitor background jobs, this should explicitly verify the process is still alive (or that a display appeared) before continuing.

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[greptile-apps]

Greptile Summary

Adds virtual display support for headless Depot macOS runners to fix XCUITest failures. Creates a 1920x1080@60Hz virtual display using the private CGVirtualDisplay API (same approach as Chromium CI) to resolve Failed to activate application (current state: Running Background) errors that occur when macOS cannot bring the app to foreground without a display.

• Implemented scripts/create-virtual-display.m - Objective-C tool that creates and maintains a virtual display using private CoreGraphics APIs
• Modified workflow to compile and launch the display tool as a background process before running tests
• Added display diagnostics before/after to verify display creation

Confidence Score: 4/5

• Safe to merge - focused CI infrastructure fix with proper error handling
• Well-tested approach (used by Chromium CI), proper error checking, scoped to CI environment only. Minor point: VDISPLAY_PID stored but unused (likely for future debugging)
• No files require special attention

Important Files Changed

Filename	Overview
scripts/create-virtual-display.m	New Objective-C tool creates 1920x1080 virtual display using private CoreGraphics API for headless CI runners
.github/workflows/test-depot.yml	Adds virtual display compilation and background execution step with before/after diagnostics

_{Last reviewed commit: 48a1dca}