Using test light to visually see spark from secondary ignition

Seen Scanner Danner use this technique and have questions about it. If I expose one ignition coil from engines with it still plugged in to test/visually see if there is spark while cranking engine. Is it recommended when using a test light to connect test light to battery positive or battery negative? Can it be done to either battery post? And why?

I have seen some videos in which a mechanic exposes the entire all-in-one 4x coil plug connected to one “solid rail”, and he used alligator clips to each coil plug boot and connected other ends to engine frame ground.

In my opinion it is not advisable to connect to the battery at all.
Spark wants a path to ground, and a gassing battery wants a spark to explode.
I connect to any metal in the engine bay.

Thank you for the response.

Also, watching “WASTE SPARK IGNITION TESTING - PRIMARY CURRENT (AUDI A6) PART 1“

Time 22:58 test light illuminates on 2x wires, one back path return to ground thro fuel pump. A schematic is briefly shown but it’s not fully displayed. I was wanting to ask if someone could share the schematic again to visually study and learn the ignition system and how the wire is tied to fuel pump.

I'm having trouble finding that video. If you would please post the link will be happy to look for the diagram for you.

www.scannerdanner.com/scannerdanner-prem...d2FzdGUtc3BhcmsiXQ==

I believe it's a 2001 audi a6 2.8L V6 30V as these use the waste spark system
 

Thank-you ! I appreciate it. You have no idea how helpful this was for me to grasp what was going on!