It depends on the application, but CLIs can make testing GUIs easier in two ways: - you can test the rendering layer in isolation by using the GUI to display t

It depends on the application, but CLIs can make testing GUIs easier in two ways: - you can test the rendering layer in isolation by using the GUI to display two pieces of information manipulated by the CLI and comparing the renders, eg blank screen -> add some object. - you can comparison test the GUI, eg pressing button X produces the same result as CLI option Y. Properly testing a GUI requires having an internal CLI, in places I’ve worked — eg, app companies.