cmux-testing

cmux-testing encodes the cmux project's testing rules for Swift Testing, test-target compilation, and package/refactor validation. It applies when adding or changing tests, touching package or refactor code, or deciding whether running reload.sh is sufficient validation. It solves a concrete correctness problem: ensuring that tests genuinely exercise runtime behavior and that changes don't silently break the test target while the app still builds.

The skill sets several policies. A regression-test commit policy uses a two-commit structure — commit 1 adds only the failing test (CI goes red), commit 2 adds the fix (CI goes green) — so the PR proves the test catches the bug. A test-quality policy forbids tests that only assert on source text, method signatures, AST fragments, grep patterns, or checked-in metadata files like Info.plist, project.pbxproj, or .xcconfig; tests must verify observable runtime behavior through executable paths, preferring the built app bundle or a runtime seam for metadata changes. Swift Testing is the default for all unit and integration tests (import Testing, @Test, @Suite, #expect, try #require, @Test(arguments:), .serialized, .tags), while UI tests stay on XCTest/XCUITest under cmuxUITests. A migration guide maps XCTest constructs to Swift Testing equivalents (XCTestCase to @Suite struct, XCTAssertEqual to #expect(a == b), XCTUnwrap to try #require, setUp/tearDown to init/deinit).

It targets contributors working on the cmux macOS codebase. It warns that reload.sh builds only the cmux scheme and does not compile the test target, so package/refactor changes should build the cmux-unit scheme (with -derivedDataPath /tmp/cmux-<tag> and, for cmuxApp/AppDelegate churn, a GlobalISel workaround flag) or rely on the tests CI job. It also documents a deterministic remote-tmux live-layout fuzz harness driven by scripts/remote-tmux-fuzz-host.sh, remote-tmux-fuzz-marathon.sh, and remote-tmux-live-fuzz.sh using the cmux-fuzzhost alias, with seed-based reproducible runs and detailed setup-failure fixes. Deeper guidance lives in references such as swift-testing-migration.md, regression-and-quality.md, and local-vs-ci-validation.md.