Visually inspecting the output in a handful of environments and hoping it generalizes to all current and future environments, because there is no way to program

Visually inspecting the output in a handful of environments and hoping it generalizes to all current and future environments, because there is no way to programmatically determine what the environment is actually doing with the content, is primitive. But it works well enough for blogs and shopping carts, so there must not be a problem.