You can do it easily, its common practice. It’s also pretty ineffective. You ever notice how VPN’s advertise you can access content outside of your geo location? Surrpise, China can do that too!

Speed tests cheat, they don’t make you download thousands of gigs of data to get a throughput. Which is exactly what you would need to do to accurately test your connection. They send a bit of data, see how fast it goes, do some calculations and assume.

ISP’s can also cheat as they can give ‘burst’ service which temporarily gives you a bump in speed. This can be advertised to you as a perk, but I don’t think many people care, or used to trick speed tests.

It’s like when your boss walks by you and you work a bit harder to appear busy.