Attempt to bind free port in word count test

Author: dwskoog

streamz/tests/test_sources.py

@@ -4,7 +4,7 @@
 from flaky import flaky
 import pytest
 from streamz import Source
-from streamz.utils_test import wait_for, await_for, gen_test
+from streamz.utils_test import free_port, wait_for, await_for, gen_test
 import socket
 
 
@@ -49,7 +49,7 @@ def test_tcp():
 
 @flaky(max_runs=3, min_passes=1)
 def test_tcp_word_count_example():
-    port = 9999
+    port = free_port()
     s = Source.from_tcp(port)
     out = s.map(bytes.split).flatten().frequencies().sink_to_list()
     s.start()

streamz/utils_test.py

@@ -4,6 +4,7 @@
 import logging
 import os
 import shutil
+import socket
 import tempfile
 from time import time, sleep
 
@@ -14,6 +15,13 @@
 from .core import _io_loops, Stream
 
 
+def free_port():
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+        s.bind(('localhost', 0))
+        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        return s.getsockname()[1]
+
+
 @contextmanager
 def tmpfile(extension=''):
     extension = '.' + extension.lstrip('.')