Function help 

pub fn help(spec: &Spec<'_>, path: &[&str], want: Page) -> String

One command’s help page, found by the words a user would type.

path names the command without the binary: &[] is the root, &["config", "ls"] is a nested one. Aliases work, because a test should be able to ask the way a user would.

Panics when the path names no command, listing what the parent does have — a test naming a command that was renamed should say so, not quietly assert about the wrong page.