I’m confused what you think a better alternative would be? If there was a test number, what if that worked, but you couldn’t call the real 911?
A test number would suffice in some situations. When an incompetent VOIP provider takes an action to block calls “for security purposes”, they cannot legally block /all/ calls. 911 calls must be permitted. And 911 test calls would obviously require the same status. I do not trust their competency. But if their call blocking allows a 911 test number through, it proves that their blockade is not a simple crude block on /everything/.
A test number would not be the only solution. With some services you can set the CID to whatever you want. So in principle a CID of 555-1212 could have special meaning to 911 receiptionists. So a tester would set the CID info to that number before calling 911.
911 is not always instantly answered by humans. When answered by a machine, there could be a cancel code. E.g. dial “119” after connecting to cancel it.
There’s no way around it: to be absolutely sure your phone can contact 911, you have to… dial 911.
Sure, if you need that extra level of certainty. In the typical cases that I mentioned (no GSM subscription), a test number would be sufficient. It would show that the dialed number reaches a switch that treats it.