add unittest skip condition for unsupported targets, remove failing a…

…ssertion from unsupported targets

test/test_server_asyncio.py

@@ -6,8 +6,6 @@
 _logger = logging.getLogger()
 if IS_PYTHON3: # Python 3
     from asynctest.mock import patch, Mock, MagicMock
-else:
-    assert(False, "asyncio is not available pre-python 3.6")
 
 from pymodbus.device import ModbusDeviceIdentification
 from pymodbus.factory import ServerDecoder
@@ -36,7 +34,7 @@
     IS_HIGH_SIERRA_OR_ABOVE = False
     SERIAL_PORT = "/dev/ptmx"
 
-
+@pytest.mark.skipif(not IS_PYTHON3, reason="requires python3.4 or above")
 class AsyncioServerTest(asynctest.TestCase):
     '''
     This is the unittest for the pymodbus.server.asyncio module