If so, it's hard to say since the server on the other end changes what it will max at. Since you upload is greater than your download, I wouldn't be shocked if it's the other side of the test not keeping up with you. Basically, with Gigabit services, it is entirely possible that you have more bandwidth than the test server.

Try the tool google fiber tool which is specifically designed for this (linked below).

However, the fact that you were only seeing 10 Mbps when you were paying for 50 Mbps is concerning that there is something else wrong. FiOS and speedtests should have had no issue delivering your 50 Mbps over just about an 5 year or newer WiFi router with a decent signal unless you live in an apartment building.

You may have an issue with packet loss. If so, what equipment is involved? From the the ONT (verizon box in your garage/basement) is it a coax or ethernet cable? If coax, do you have a G1100 "Quantum" Gateway/Router? Could be you have an old gateway from before your upgrade? If ethernet, what WiFi Router do you have? From the gateway, how old are your ethernet cables? Do you know if they are Cat 5/5e/6 (would be printed on it)? They could be unnoticeably damaged.