If you want to do an ongoing speedtest with graphs for up- and download, forget about the web-based tools like speedtest.net and fast.com - those are nice if you are on a mobile phone. These speedtests as a service will not show you continuous graphs (which sometime you might want to have if you are tweaking your network).
On such occasions, your *nix shell yields better tooling!
First, fire up a Terminal and start
nload to view network traffic. If you are on macOS, you can also use the graphical tool
Then, in a second Terminal, start a...