Allow sanic test client to bind to a random port

docs/sanic/testing.md

@@ -59,6 +59,23 @@ the available arguments to aiohttp can be found
 [in the documentation for ClientSession](https://aiohttp.readthedocs.io/en/stable/client_reference.html#client-session).
 
 
+## Using a random port
+
+If you need to test using a free unpriveleged port chosen by the kernel
+instead of the default with `SanicTestClient`, you can do so by specifying
+`port=None`. On most systems the port will be in the range 1024 to 65535.
+
+```python
+# Import the Sanic app, usually created with Sanic(__name__)
+from external_server import app
+from sanic.testing import SanicTestClient
+
+def test_index_returns_200():
+    request, response = SanicTestClient(app, port=None).get('/')
+    assert response.status == 200
+```
+
+
 ## pytest-sanic
 
 [pytest-sanic](https://github.com/yunstanford/pytest-sanic) is a pytest plugin, it helps you to test your code asynchronously.

sanic/testing.py

@@ -3,6 +3,7 @@
 from sanic.exceptions import MethodNotSupported
 from sanic.log import logger
 from sanic.response import text
+from socket import socket
 
 
 HOST = "127.0.0.1"
@@ -11,19 +12,13 @@
 
 class SanicTestClient:
     def __init__(self, app, port=PORT):
+        """Use port=None to bind to a random port"""
         self.app = app
         self.port = port
 
-    async def _local_request(self, method, uri, cookies=None, *args, **kwargs):
+    async def _local_request(self, method, url, cookies=None, *args, **kwargs):
         import aiohttp
 
-        if uri.startswith(("http:", "https:", "ftp:", "ftps://" "//")):
-            url = uri
-        else:
-            url = "http://{host}:{port}{uri}".format(
-                host=HOST, port=self.port, uri=uri
-            )
-
         logger.info(url)
         conn = aiohttp.TCPConnector(ssl=False)
         async with aiohttp.ClientSession(
@@ -79,19 +74,35 @@ async def error_handler(request, exception):
             else:
                 return self.app.error_handler.default(request, exception)
 
+        if self.port:
+            server_kwargs = dict(host=HOST, port=self.port, **server_kwargs)
+            host, port = HOST, self.port
+        else:
+            sock = socket()
+            sock.bind((HOST, 0))
+            server_kwargs = dict(sock=sock, **server_kwargs)
+            host, port = sock.getsockname()
+
+        if uri.startswith(("http:", "https:", "ftp:", "ftps://", "//")):
+            url = uri
+        else:
+            url = "http://{host}:{port}{uri}".format(
+                host=host, port=port, uri=uri
+            )
+
         @self.app.listener("after_server_start")
         async def _collect_response(sanic, loop):
             try:
                 response = await self._local_request(
-                    method, uri, *request_args, **request_kwargs
+                    method, url, *request_args, **request_kwargs
                 )
                 results[-1] = response
             except Exception as e:
                 logger.exception("Exception")
                 exceptions.append(e)
             self.app.stop()
 
-        self.app.run(host=HOST, debug=debug, port=self.port, **server_kwargs)
+        self.app.run(debug=debug, **server_kwargs)
         self.app.listeners["after_server_start"].pop()
 
         if exceptions:

tests/test_test_client_port.py

@@ -0,0 +1,34 @@
+import socket
+
+from sanic.testing import PORT, SanicTestClient
+from sanic.response import json, text
+
+# ------------------------------------------------------------ #
+#  UTF-8
+# ------------------------------------------------------------ #
+
+
+def test_test_client_port_none(app):
+    @app.get('/get')
+    def handler(request):
+        return text('OK')
+
+    test_client = SanicTestClient(app, port=None)
+
+    request, response = test_client.get('/get')
+    assert response.text == 'OK'
+
+    request, response = test_client.post('/get')
+    assert response.status == 405
+
+
+def test_test_client_port_default(app):
+    @app.get('/get')
+    def handler(request):
+        return json(request.transport.get_extra_info('sockname')[1])
+
+    test_client = SanicTestClient(app)
+    assert test_client.port == PORT
+
+    request, response = test_client.get('/get')
+    assert response.json == PORT