Test AudioContext activeSourceCount and AudioBufferSourceNode playbackState.

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".

PASS Rendering time is 2 seconds.
PASS UNSCHEDULED_STATE Source has been created
PASS SCHEDULED_STATE   3 second source scheduled to start at time 3
PASS PLAYING_STATE     2 second source starting at time 1
PASS FINISHED_STATE    1.25 second source starting at time 0
PASS SCHEDULED_STATE   1 second grain scheduled to start at time 3
PASS PLAYING_STATE     2 second grain starting at time 0.5
PASS FINISHED_STATE    1 second grain starting at time 0.5
PASS SCHEDULED_STATE   a looping 0.5 second source scheduled at time 3
PASS PLAYING_STATE     a looping 0.5 second source starting at time 1.25
PASS 3 are currently playing as expected.
PASS activeSourceCount and playbackState tests succeeded.
PASS successfullyParsed is true

TEST COMPLETE