When you do the connection test you first need to make sure that you have granted access to your browser to access both your camera and microphone.
For your chrome browser you can find more information on how to check your permissions here: Fix your camera permissions!
It is important to make sure that you have no firewalls, antivirus, ad-blockers and pop-up blockers running that may be preventing your camera and microphone from turning on. There are also reports of certain types of USB devices affecting the Video quality, so make sure these are not compromising your test.
Next you will see three loading bars below your video screen that indicate your video, audio, and packet loss quality.
If you are experiencing a loss in audio or video and a high packet loss than you may need to try and optimize your internet connection. Packet loss in this instance means information you are trying to send is being lost in transit - the lower the packet loss the better.
Packet loss can be experienced for a variety of reasons, but generally it could be to do with your hardware or your ISP connection. If you leave your computer and router on for long periods of time they can become overburdened with data from past sessions, it's a good idea to try and turn these off or restart them regularly.
If resetting your hardware brings no noticeable difference to your connection test than you may need to discuss your connection with your ISP. Your ISP could have the ability to alter the bandwidth of your connection and the priority of your connection so it is more optimized for video and audio calls.