What is the best way to test for missing or unknown commands? Is the existing support good enough?

Research prompted by Commander v4 which changes program.args and will break some client code which was dependent on the previous behaviour: #1048

Example of affected code: #7 (comment)

Related issues:

• Show help if no command was executed #7 Show help if no command was executed
• Support to know if any known command was processed, or any output written #240 Support to know if any known command was processed, or any output written
• How to detect an unsupported command? #338 How to detect an unsupported command? [git-style]
• running an unknown subcommand does not fail #432 running an unknown subcommand does not fail
• Show help when command is unknown #603 Show help when command is unknown
• Using sub-command always invokes *  #809 Using sub-command always invokes *
• argments are empty #940 argments are empty
• Throw error when no sub-command specified #942 Throw error when no sub-command specified
• It looks not way to know has action is run? #977 It looks not way to know has action is run?
• Top level command action does not work. #978 Top level command action does not work
• Passing command option leaves content in args #1032 Passing command option leaves content in args