Add testing library to patch dependencies in unittests

  - Since there needs to be a support for python 2.7, 3.5 and 3.6 the
  default unittest.mock will not work. The dependency "mock" makes it
  work but it forced to rename the already existing mock.py (so it can
  be properly imported)

Author: krimvp

mock.py app_mock.pymock.py renamed to app_mock.py

@@ -5,3 +5,4 @@ pycodestyle
 grpcio==1.7.3
 protobuf
 googleapis-common-protos
+mock==2.0.0

requirements.txt

@@ -5,7 +5,7 @@
 
 
 import unittest
-from mock import MockApplicationManager
+from app_mock import MockApplicationManager
 from ttn import ApplicationClient
 import ttn.github_com.TheThingsNetwork.api.handler.handler_pb2 as handler
 from ttn.utils import stubs

test_application.py

@@ -4,7 +4,7 @@
 # MIT license that can be found in the LICENSE file.
 
 import unittest
-from unittest.mock import patch
+from mock import patch
 
 from ttn import DiscoveryClient
 
@@ -15,15 +15,15 @@ def test_constructor_discovery(self):
         self.discovery = DiscoveryClient()
         assert hasattr(self.discovery, "client")
 
-    def test_default_insecure_channel_set_to_false(self):
-        with patch("grpc.secure_channel") as mock_grpc_secure_channel:
-            self.discovery = DiscoveryClient()
-            assert mock_grpc_secure_channel.call_count == 1
+    @patch("grpc.secure_channel")
+    def test_default_insecure_channel_set_to_false(self, mock_grpc_secure_channel):
+        self.discovery = DiscoveryClient()
+        assert mock_grpc_secure_channel.call_count == 1
 
-    def test_insecure_channel_called(self):
-        with patch("grpc.insecure_channel") as mock_grpc_insecure_channel:
-            self.discovery = DiscoveryClient(insecure_channel=True)
-            assert mock_grpc_insecure_channel.call_count == 1
+    @patch("grpc.insecure_channel")
+    def test_insecure_channel_called(self,mock_grpc_insecure_channel):
+        self.discovery = DiscoveryClient(insecure_channel=True)
+        assert mock_grpc_insecure_channel.call_count == 1
 
     def test_get_by_app_id(self):
         self.discovery = DiscoveryClient()