Write regression tests that (1) are portable across platforms where behavior is shared and (2) are “behaviorally decisive,” meaning they must fail if the real logic is removed. Apply: - Use broad `cfg` gates for shared behavior (e.g., `#[cfg(unix)]`) rather than narrow OS-specific gates in core modules. - Shape fixtures so the expected state transition is not satisfied by index coincidences or incidental setup. If your code must “reconcile” selection/focus after deletion or shifting, pick a scenario where indices change and the reconciliation block is required. Example (portability + decisive setup): ```rust #[cfg(unix)] #[test] fn preserves_selection_after_close_requiring_reconciliation() { // Arrange: 3 workspaces so the survivor index shifts // e.g., [background (only tab), middle, active (selected)] // Act: close background's last tab // Assert: selected workspace is updated by reconciliation logic, // and the test would fail if focus/selection reconciliation were removed. } ``` This standard prevents flaky/overly restrictive platform gating and ensures regression tests actually guard the behavior you care about.