Fixed unused_tcp_port_factory edge condition. Added a test for it.

pytest_asyncio/plugin.py

@@ -97,8 +97,11 @@ def unused_tcp_port_factory():
 
     def factory():
         port = unused_tcp_port()
+
         while port in produced:
-            port = unused_tcp_port
+            port = unused_tcp_port()
+
+        produced.add(port)
 
         return port
     return factory

tests/test_simple.py

@@ -3,6 +3,8 @@
 import os
 import pytest
 
+import pytest_asyncio.plugin
+
 
 @asyncio.coroutine
 def async_coro(loop):
@@ -106,6 +108,26 @@ def closer(_, writer):
     yield from server3.wait_closed()
 
 
+def test_unused_port_factory_duplicate(unused_tcp_port_factory, monkeypatch):
+    """Test correct avoidance of duplicate ports."""
+    counter = 0
+
+    def mock_unused_tcp_port():
+        """Force some duplicate ports."""
+        nonlocal counter
+        counter += 1
+        if counter < 5:
+            return 10000
+        else:
+            return 10000 + counter
+
+    monkeypatch.setattr(pytest_asyncio.plugin, 'unused_tcp_port',
+                        mock_unused_tcp_port)
+
+    assert unused_tcp_port_factory() == 10000
+    assert unused_tcp_port_factory() > 10000
+
+
 class Test:
     """Test that asyncio marked functions work in test methods."""