Change channel tests to use public API

This allows for testing other implementations of grpc.Server.

src/python/grpcio_tests/tests/unit/_channel_connectivity_test.py

@@ -34,8 +34,6 @@ import time
 import unittest
 
 import grpc
-from grpc import _channel
-from grpc import _server
 from tests.unit.framework.common import test_constants
 from tests.unit import _thread_pool
 
@@ -78,7 +76,7 @@ class ChannelConnectivityTest(unittest.TestCase):
   def test_lonely_channel_connectivity(self):
     callback = _Callback()
 
-    channel = _channel.Channel('localhost:12345', (), None)
+    channel = grpc.insecure_channel('localhost:12345')
     channel.subscribe(callback.update, try_to_connect=False)
     first_connectivities = callback.block_until_connectivities_satisfy(bool)
     channel.subscribe(callback.update, try_to_connect=True)
@@ -105,13 +103,13 @@ class ChannelConnectivityTest(unittest.TestCase):
 
   def test_immediately_connectable_channel_connectivity(self):
     thread_pool = _thread_pool.RecordingThreadPool(max_workers=None)
-    server = _server.Server(thread_pool, (), ())
+    server = grpc.server(thread_pool)
     port = server.add_insecure_port('[::]:0')
     server.start()
     first_callback = _Callback()
     second_callback = _Callback()
 
-    channel = _channel.Channel('localhost:{}'.format(port), (), None)
+    channel = grpc.insecure_channel('localhost:{}'.format(port))
     channel.subscribe(first_callback.update, try_to_connect=False)
     first_connectivities = first_callback.block_until_connectivities_satisfy(
         bool)
@@ -146,12 +144,12 @@ class ChannelConnectivityTest(unittest.TestCase):
 
   def test_reachable_then_unreachable_channel_connectivity(self):
     thread_pool = _thread_pool.RecordingThreadPool(max_workers=None)
-    server = _server.Server(thread_pool, (), ())
+    server = grpc.server(thread_pool)
     port = server.add_insecure_port('[::]:0')
     server.start()
     callback = _Callback()
 
-    channel = _channel.Channel('localhost:{}'.format(port), (), None)
+    channel = grpc.insecure_channel('localhost:{}'.format(port))
     channel.subscribe(callback.update, try_to_connect=True)
     callback.block_until_connectivities_satisfy(_ready_in_connectivities)
     # Now take down the server and confirm that channel readiness is repudiated.

src/python/grpcio_tests/tests/unit/_channel_ready_future_test.py

@@ -33,8 +33,6 @@ import threading
 import unittest
 
 import grpc
-from grpc import _channel
-from grpc import _server
 from tests.unit.framework.common import test_constants
 from tests.unit import _thread_pool
 
@@ -79,7 +77,7 @@ class ChannelReadyFutureTest(unittest.TestCase):
 
   def test_immediately_connectable_channel_connectivity(self):
     thread_pool = _thread_pool.RecordingThreadPool(max_workers=None)
-    server = _server.Server(thread_pool, (), ())
+    server = grpc.server(thread_pool)
     port = server.add_insecure_port('[::]:0')
     server.start()
     channel = grpc.insecure_channel('localhost:{}'.format(port))