Formats a test id for titles, plans and --grep. Padding to a fixed width means "#0012" can never match "#00120" or "#0112".
--grep
a positive whole number
"#" plus at least four digits: 12 → "#0012", 12345 → "#12345"
"#"
12
"#0012"
12345
"#12345"
Error if id is not a positive whole number
id
Formats a test id for titles, plans and
--grep. Padding to a fixed width means "#0012" can never match "#00120" or "#0112".