I think some of it is bad wording - bad engrish laugh

https://blog.bavauto.com/7321/new-diagnostic-tool-inductive-spark-tester-for-bmw-mini-and-others/ .

This site just says you need to have the engine turning over

but it begs the question, how does one hold it on the lead whilst pulling the cord on a mower

An inline tester is so much easier - or just remove the plug

Would be handy for finding a miss in a multi cylinder engine though