refactor: check connection connected before append to free list when release it

Author: waketzheng

asyncodbc/pool.py

@@ -192,7 +192,7 @@ async def release(self, conn):
             self._terminated.remove(conn)
             return
         self._used.remove(conn)
-        if not conn.closed:
+        if conn.connected and not conn.closed:
             if self._closing:
                 await conn.close()
             else:

tests/test_pool.py

@@ -52,6 +52,14 @@ async def test_release(pool):
         await pool.release(conn)
     assert 1 == pool.freesize
     assert not pool._used
+    assert conn in pool._free
+
+    conn2 = await pool.acquire()
+    try:
+        await conn2.close()
+    finally:
+        await pool.release(conn2)
+    assert conn2 not in pool._free
 
 
 @pytest.mark.asyncio