Read this: https://mariners.coastguard.blog/2020/10/19/performing-a-vhf-marine-radio-check/.
Read this https://www.dco.uscg.mil/Portals/9/DCO%20Documents/5p/MSIB/2020/MSIB-20-20.pdf.

Print a copy or two, put them in your standard operating procedures.
Also see the Rescue 21 for Boaters list: https://www.dcms.uscg.mil/Our-Organization/Assistant-Commandant-for-Acquisitions-CG-9/Programs/C4ISR-Programs/Rescue-21/Rescue-21-for-Boaters/
I've got the 00366999 MMSI number programmed into my radio. I call it. I get an answer. That confirms my radio works.
I don't need to page random strangers on CH 16 to check my radio.
If you want to hail us, our MMSI is 367449760.