Modem play audio (wav file) fails

[emxsys]

After the port to Python3, the Modem class fails to play the audio file. The system stalls.
Following is the output of the Modem unit tests after pressing Ctrl-C

(python3) pi@hamshack:~/src/callattendant/src $ python hardware/modem.py
[Configuration]
  BLOCKED_ACTIONS = ('play_message',)
  BLOCKED_MESSAGE_FILE = hardware/blocked.wav
  BLOCK_ENABLED = True
  BLOCK_NAME_PATTERNS = {'V[0-9]{15}': 'Telemarketer Caller ID'}
  BLOCK_NUMBER_PATTERNS = {}
  DATABASE = callattendant.db
  DEBUG = False
  DEBUGs = True
  ENV = production
  ROOT_PATH = /home/pi/src/callattendant/src
  SCREENING_MODE = ('whitelist', 'blacklist')
  TESTING = False
Running Unit Tests....
Modem COM Port is: /dev/ttyACM0
Assert factory reset
Assert display modem settings
Assert put modem into voice mode.
Assert set compression method and sampling rate specifications.
Assert put modem into TAD mode.
Assert put modem into data transmit state.
Assert cancel data transmit state.
Play Audio Msg - Start
Play Audio Msg - playing wav file
^CTraceback (most recent call last):
  File "hardware/modem.py", line 563, in <module>
    sys.exit(test(config, phone_ringing, handle_caller))
  File "hardware/modem.py", line 534, in test
    modem.play_audio(os.path.join(currentdir, "sample.wav"))
  File "hardware/modem.py", line 234, in play_audio
    time.sleep(.12)
KeyboardInterrupt