CallDistanceTransceiver.py: make DummyModem look more like Modem

The "response" argument is optional in the get_response() method, this
avoids getting an error when trying to transmit with DummyModem:

  TypeError: get_response() missing 1 required positional argument: 'response'

diff --git a/src/savemysugar/CallDistanceTransceiver.py b/src/savemysugar/CallDistanceTransceiver.py
index 588c985..6361afa 100755 (executable)
--- a/src/savemysugar/CallDistanceTransceiver.py
+++ b/src/savemysugar/CallDistanceTransceiver.py
@@ -424,7 +424,7 @@ def test_send_receive():
         def send_command(self, command):
             pass
 
-        def get_response(self, response):
+        def get_response(self, response=None):
             # pylint: disable=unused-argument
 
             setup_time = random.uniform(self.transceiver.modulator.period_min,