Fix: Avoid warning on latest Pytest versions

Pytest added a deprecation warning to signal fixtures being called
directly as functions.

Ref: pytest-dev/pytest#3661
Ref: https://docs.pytest.org/en/latest/deprecations.html#calling-fixtures-directly

pytest_asyncio/plugin.py

@@ -174,25 +174,29 @@ def event_loop(request):
     loop.close()
 
 
-@pytest.fixture
-def unused_tcp_port():
+def _unused_tcp_port():
     """Find an unused localhost TCP port from 1024-65535 and return it."""
     with contextlib.closing(socket.socket()) as sock:
         sock.bind(('127.0.0.1', 0))
         return sock.getsockname()[1]
 
 
+@pytest.fixture
+def unused_tcp_port():
+    return _unused_tcp_port()
+
+
 @pytest.fixture
 def unused_tcp_port_factory():
     """A factory function, producing different unused TCP ports."""
     produced = set()
 
     def factory():
         """Return an unused port."""
-        port = unused_tcp_port()
+        port = _unused_tcp_port()
 
         while port in produced:
-            port = unused_tcp_port()
+            port = _unused_tcp_port()
 
         produced.add(port)
 

tests/test_simple.py

@@ -104,7 +104,7 @@ def mock_unused_tcp_port():
         else:
             return 10000 + counter
 
-    monkeypatch.setattr(pytest_asyncio.plugin, 'unused_tcp_port',
+    monkeypatch.setattr(pytest_asyncio.plugin, '_unused_tcp_port',
                         mock_unused_tcp_port)
 
     assert unused_tcp_port_factory() == 10000

tox.ini

@@ -4,7 +4,7 @@ minversion = 2.5.0
 
 [testenv]
 extras = testing
-commands = coverage run -m pytest {posargs}
+commands = coverage run -m pytest -W error {posargs}
 
 [testenv:coverage-report]
 deps = coverage