How to confirm VPN is working properly?

I’ve just started using a VPN service because I’m doing work from a hotel room for an extended period of time with an iMac connected to the hotel’s open wifi. Hotel has a web log-in with password, but no encryption.

I installed a personal VPN service and it appears to be working properly, but when I turn off the VPN the internet connection continues to function without any indication. It appears that if I upgrade to the next level provided by this VPN service, there is a "kill-switch" option, which I assume blocks the internet connection when the VPN is off. The service I’m using basically has a connect/disconnect feature, and a map of the available VPN servers. It automatically configured the VPN settings in "Network". I can see the sent/received packets when I look at the VPN settings.

However, my question is whether there is a straight-forward way for me to confirm that all of my internet traffic is going through the VPN, when the VPN is enabled? This may seem like a silly question, but if I can’t tell the difference between VPN or NO VPN, then what’s to say that some data is bypassing VPN encryption and going straight onto the unencrypted open wifi?