This page lets you select both camera and microphone inputs to check that they’re working as expected. Unfortunately, the Safari browser doesn’t currently support the microphone input, so use Firefox or another browser for this test.
If you allowed this page to access the camera just a moment ago, a live feed from the selected camera should appear below.
Similarly to the camera, a permission prompt just asked you to allow access to the microphone. If granted, a bar below should react to sound. (Note: not supported on Safari yet).