Pure-reference catalog of desktop GUI test strategies across Windows, macOS, and Linux. Defines the three accessibility-tree backends (Microsoft UI Automation on Windows, Apple Accessibility / XCTest on macOS, AT-SPI on Linux), the wrapper-tools that drive each backend (WinAppDriver, Appium-Windows, XCUIApplication, AT-SPI clients), the cross-toolkit Electron + Qt paths, and a per-OS decision matrix with accessibility-first locator strategy. Deep operational detail (per-OS asynchronous-wait hierarchies, parallel-test policy, foreground-lock / UAC / TCC / AT-SPI elevation hazards, and the high-DPI / per-monitor test matrix) lives in references/. Use as the strategic reference before picking a desktop test stack, ahead of the per-tool implementation skills.