Testing the camera
Press Start camera and allow access when the browser asks. The preview shows what the other people on a call would see, mirrored as video apps show you to yourself. Underneath is the resolution and frame rate the camera is sending. With more than one camera, pick another from the list.
Testing the microphone
Press Start microphone and speak at a normal volume: the bar should reach the middle. If it barely moves, the wrong microphone may be picked, or it is muted in your system settings. Record 5 seconds lets you hear yourself back, to check for echo, hiss or a muffled sound.
If nothing appears
If you refused access, click the camera or lock icon in the address bar, allow the camera and microphone for this site, and press Start again. If the camera is in use by another app, such as a video call left open, close that first. On a Mac, also check System Settings › Privacy & Security.
Questions
Is my video or voice recorded or sent anywhere?
No. The preview and the meter work inside this page only. The 5-second test recording stays in the page so you can play it, and is gone when you close it.
Why is my camera's resolution lower than it should be?
Browsers ask for a sensible size by default and some cameras send less in poor light. Video apps do the same, so this is close to what a call would show.