1. Verify that random frequencies are played when clicking the "Play game" button.
The panning of the sounds should change with time on most browsers.

2. Verify that a rising note is played when clicking the "Play rising note" button.
The volume and frequency should rise.

3. Verify that a falling note is played when clicking the "Play falling note" button.
The volume and frequency should fall.

4. Verify that multiple notes are played in sync when clicking the "Play music"
button. The music should fade in. Note that clicking the other buttons while the
music is playing will interrupt some of the instruments playing the music.
