Add integration test for python greeter server.

examples/helloworld/python/BUILD

@@ -17,9 +17,24 @@ py_binary(
 
 py_binary(
     name = "greeter_server",
+    srcs = [":grpc_server"],
+)
+
+py_test(
+    name = "test_greeter_server",
+    srcs = ["test_greeter_server.py"],
+    deps = [":grpc_server"]
+)
+
+# This library is necessary for creating py_test cases o/w if we explicitly add
+# "//examples/helloworld/proto:py" in the 'deps' list then bazel complains with:
+# "'//examples/helloworld/proto:py' does not have mandatory provider 'py'".
+# It's also useful for packaging all the server code in a lib to reuse for the :greeter_server.
+py_library(
+    name = "grpc_server",
     srcs = [
         "greeter_server.py",
         "//examples/proto:py",
         "//examples/helloworld/proto:py",
-    ],
-)
+    ]
+)

examples/helloworld/python/test_greeter_server.py

@@ -0,0 +1,39 @@
+import unittest
+
+import grpc
+import greeter_server
+
+from examples.helloworld.proto import helloworld_pb2
+
+
+def _get_random_port():
+    import socket
+    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s.bind(("", 0))
+    s.listen(1)
+    port = s.getsockname()[1]
+    s.close()
+    return port
+
+TEST_PORT = _get_random_port()
+
+
+class GreeterServerTest(unittest.TestCase):
+    _server = None
+    _client = None
+
+    def setUp(self):
+        self._server = greeter_server._GreeterServer(greeter_server._GreeterService(), TEST_PORT)
+        self._server.start()
+        channel = grpc.insecure_channel('localhost:{port}'.format(port=TEST_PORT))
+        self._client = helloworld_pb2.GreeterStub(channel)
+
+    def tearDown(self):
+        self._server.stop()
+
+    def test_sayhello(self):
+        hello_reply = self._client.SayHello(helloworld_pb2.HelloRequest(name='you'))
+        self.assertEqual(hello_reply.message, 'Hello you')
+
+if __name__ == '__main__':
+    unittest.main()