cmux Testing

Regression test commit policy

A regression test for a bug fix ships as two commits so CI proves the test catches the bug:

1. The failing test only, no fix. CI goes red.
2. The fix. CI goes green.

The GitHub PR Commits tab then shows the test genuinely fails without the fix.

Test wiring

Test files in cmuxTests/ must be wired into cmux.xcodeproj/project.pbxproj with a matching PBXFileReference and PBXSourcesBuildPhase entry. A .swift file added without them is silently ignored by Xcode: xcodebuild test -only-testing:cmuxTests/<TestClass> and bot reviews both pass with "Executed 0 tests", so the missing wiring is indistinguishable from a clean red/green regression test until a real user hits the bug. Surfaced during https://github.com/manaflow-ai/cmux/issues/4529 against https://github.com/manaflow-ai/cmux/pull/4536.

The workflow-guard-tests CI job runs ./scripts/lint-pbxproj-test-wiring.sh. Add the file through Xcode (drag into the cmuxTests target) or hand-edit the pbxproj entries using a wired sibling such as cmuxTests/TabManagerUnitTests.swift as the template.

Test quality policy

• No tests that only verify source text, method signatures, AST fragments, or grep-style patterns.
• No tests that read checked-in metadata or project files (Resources/Info.plist, project.pbxproj, .xcconfig, source files) just to assert a key, string, plist entry, or snippet exists.
• Tests verify observable runtime behavior through executable paths (unit, integration, e2e, CLI), not implementation shape.
• For metadata changes, verify the built app bundle or the runtime behavior that depends on the metadata.
• If a behavior cannot be exercised end to end yet, add a small runtime seam or harness first, then test through it.
• If no meaningful behavioral or artifact-level test is practical, skip the fake regression test and say so.

Test framework

Swift Testing (Swift 6 / Xcode 16) is the default for every unit and integration test: import Testing, @Test, @Suite, #expect(...), try #require(...). Do not write new import XCTest tests except UI tests.

• UI tests stay on XCTest/XCUITest. Swift Testing has no XCUIApplication integration. Files under cmuxUITests/ keep XCTestCase; do not migrate or bridge them.
• New test targets start on Swift Testing. Every new package's Tests/<Name>Tests/ ships with it from the first commit; Xcode 16 auto-detects the framework from import Testing with no Package.swift configuration.
• Parameterized tests use @Test(arguments: [...]) instead of duplicate methods.
• Parallelization. Swift Testing runs tests in parallel by default, including across suites. A suite that needs ordering or guards shared mutable state gets .serialized, not locks or sleeps.
• Tags via @Test(.tags(.something)) let CI and local runs filter selectively.
• Migrate an existing XCTest file in place only when an edit already crosses it. Mapping in references/swift-testing-migration.md.

Test target validation

reload.sh builds only the cmux scheme, so a green reload says nothing about whether cmuxTests/cmuxUITests still compile. A moved or renamed symbol can keep the app building while breaking the test target (real case: a write(to:atomically:) typo and a removed TabManager.CommandResult surfaced only in the tests job). Before pushing package/refactor changes, build the cmux-unit scheme with -derivedDataPath /tmp/cmux-<tag> (plus the GlobalISel workaround flag for cmuxApp/AppDelegate churn), or let the tests CI job gate it.

Detailed references

• references/swift-testing-migration.md: XCTest to Swift Testing conversion mapping.
• references/regression-and-quality.md: deciding whether a test is behavioral enough.
• references/local-vs-ci-validation.md: choosing between reload.sh, cmux-unit, GitHub Actions, E2E/UI tests, and Python socket tests.
• references/remote-tmux-sizing-e2e.md: the remote-tmux mirror sizing UI suite, its ssh shim, the remote.tmux.pane_grids / remote.tmux.test_exec debug verbs, and the live layout fuzz harness.