Tests fail with Unterminated string starting at: line 1 column 90 (char 89)

[karthiknadig]

There is no exact repro steps. While creating this bug, the issue was hit while running unhandled exception tests.

Py 3.4:

Traceback (most recent call last):
  File "/opt/python/3.4.6/lib/python3.4/threading.py", line 911, in _bootstrap_inner
    self.run()
  File "/opt/python/3.4.6/lib/python3.4/threading.py", line 859, in run
    self._target(*self._args, **self._kwargs)
  File "/home/travis/build/Microsoft/ptvsd/tests/helpers/debugsession.py", line 283, in _listen
    for msg in self._conn.iter_messages():
  File "/home/travis/build/Microsoft/ptvsd/tests/helpers/debugsession.py", line 92, in iter_messages
    yield parse_message(msg)
  File "/home/travis/build/Microsoft/ptvsd/tests/helpers/vsc/_vsc.py", line 24, in parse_message
    data = json.loads(msg)
  File "/opt/python/3.4.6/lib/python3.4/json/__init__.py", line 318, in loads
    return _default_decoder.decode(s)
  File "/opt/python/3.4.6/lib/python3.4/json/decoder.py", line 343, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/opt/python/3.4.6/lib/python3.4/json/decoder.py", line 359, in raw_decode
    obj, end = self.scan_once(s, idx)
ValueError: Unterminated string starting at: line 1 column 90 (char 89)

Py 3.5-3.7:

Traceback (most recent call last):
  File "/opt/python/3.7-dev/lib/python3.7/threading.py", line 917, in _bootstrap_inner
    self.run()
  File "/opt/python/3.7-dev/lib/python3.7/threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "/home/travis/build/Microsoft/ptvsd/tests/helpers/debugsession.py", line 283, in _listen
    for msg in self._conn.iter_messages():
  File "/home/travis/build/Microsoft/ptvsd/tests/helpers/debugsession.py", line 92, in iter_messages
    yield parse_message(msg)
  File "/home/travis/build/Microsoft/ptvsd/tests/helpers/vsc/_vsc.py", line 24, in parse_message
    data = json.loads(msg)
  File "/opt/python/3.7-dev/lib/python3.7/json/__init__.py", line 355, in loads
    return _default_decoder.decode(s)
  File "/opt/python/3.7-dev/lib/python3.7/json/decoder.py", line 340, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/opt/python/3.7-dev/lib/python3.7/json/decoder.py", line 356, in raw_decode
    obj, end = self.scan_once(s, idx)
json.decoder.JSONDecodeError: Unterminated string starting at: line 1 column 90 (char 89)