Function help_tree 

pub fn help_tree(spec: &Spec<'_>, want: Page) -> String

Every command’s help page, depth-first, in one string.

The drift test: snapshot this, and any change to any page of any command — a flag’s help, a new subcommand, a heading that moved — shows up as a diff in one place. Hidden commands are included and marked, since a hidden command still has a page that can regress.