Adding examples as pytest tests

- This way they will be included in CI checks
- Decreased the delay time in the thread-like examples to speed up tests
(probably could decrease the time some more)
- Added an async version of the calculator test
- Forcing python3 support for example scripts

test/test_examples.py

@@ -0,0 +1,52 @@
+import gc
+import os
+import socket
+import subprocess
+import sys  # add examples dir to sys.path
+import time
+
+examples_dir = os.path.join(os.path.dirname(__file__), '..', 'examples')
+
+
+def run_subprocesses(address, server, client):
+    server = subprocess.Popen([os.path.join(examples_dir, server), address])
+    time.sleep(1)  # Give the server some small amount of time to start listening
+    client = subprocess.Popen([os.path.join(examples_dir, client), address])
+
+    ret = client.wait()
+    server.kill()
+    assert ret == 0
+
+
+def test_async_calculator_example():
+    address = 'localhost:36432'
+    server = 'async_calculator_server.py'
+    client = 'async_calculator_client.py'
+    run_subprocesses(address, server, client)
+
+
+def test_thread_example():
+    address = 'localhost:36433'
+    server = 'thread_server.py'
+    client = 'thread_client.py'
+    run_subprocesses(address, server, client)
+
+
+def test_addressbook_example():
+    proc = subprocess.Popen([os.path.join(examples_dir, 'addressbook.py')])
+    ret = proc.wait()
+    assert ret == 0
+
+
+def test_async_example():
+    address = 'localhost:36434'
+    server = 'async_server.py'
+    client = 'async_client.py'
+    run_subprocesses(address, server, client)
+
+
+def test_ssl_async_example():
+    address = 'localhost:36435'
+    server = 'async_ssl_server.py'
+    client = 'async_ssl_client.py'
+    run_subprocesses(address, server, client)