fix: Have httpstan use an unused port

Closes #94

stan/common.py

@@ -1,6 +1,7 @@
 """Common routines"""
 import asyncio
 import contextlib
+import socket
 import threading
 import time
 import typing
@@ -19,7 +20,15 @@ class ServerAddress(typing.NamedTuple):
 @contextlib.contextmanager
 def httpstan_server():
     """Manage starting and stopping an httpstan web gateway."""
-    host, port = "127.0.0.1", 8080
+
+    def unused_port():
+        s = socket.socket()
+        s.bind(("127.0.0.1", 0))
+        port = s.getsockname()[1]
+        s.close()
+        return port
+
+    host, port = "127.0.0.1", unused_port()
     runner = aiohttp.web.AppRunner(httpstan.app.make_app())
     loop = asyncio.get_event_loop()
 

tests/test_httpstan_unused_port.py

@@ -1,7 +1,6 @@
 import socket
 
 import requests
-import pytest
 
 import stan
 
@@ -10,11 +9,10 @@ def test_httpstan_port_conflict():
     s = socket.socket()
     try:
         s.bind(("", 8080))
-        with pytest.raises(OSError) as excinfo:
-            with stan.common.httpstan_server() as server:
-                host, port = server.host, server.port
-                response = requests.get(f"http://{host}:{port}/v1/health")
-                assert response.status_code == 200
-            assert "address already in use" in str(excinfo.value)
+        with stan.common.httpstan_server() as server:
+            host, port = server.host, server.port
+            response = requests.get(f"http://{host}:{port}/v1/health")
+            assert response.status_code == 200
+            assert port != 8080
     finally:
         s.close()