From the linked FAQ:

How can I make a test 9-1-1 call? To make a test 9-1-1 call, you need to first contact the 9-1-1 center that serves your area. The non-emergency numbers for Colorado's 9-1-1 centers are available here(opens in new window). If you're unsure which 9-1-1 center serves your area, call the 911 Program at 303-894-2871, and we'll help you identify the 9-1-1 center for the location you want to test from.

When you call the 9-1-1 center, ask them if it would be okay to make a test 9-1-1 call. If they are particularly busy or are handling a major incident, they may ask you to call back at a later time.

When your phone cannot make normal calls for whatever reason¹, you obviously want to know if 911 calls will at least work. And the idiots design a test procedure that requires normal phone calls to work.

① Typical reasons why you may be unable to make normal calls:

• You have a GSM phone with no GSM chip, or unsubscribed chip.
• You are on a prepaid plan and have no credit.

So indeed the telecom industry has a glaring competency problem.