slightly simplify collection node init

pytest/plugin/pytester.py

@@ -275,6 +275,7 @@ class TmpTestdir:
         p.ensure("__init__.py")
         return p
 
+    Collection = Collection
     def getnode(self, config, arg):
         collection = Collection(config)
         return collection.getbyid(collection._normalizearg(arg))[0]

pytest/plugin/session.py

@@ -324,7 +324,7 @@ class Node(object):
         self.config = config or parent.config
 
         #: the collection this node is part of.
-        self.collection = collection or getattr(parent, 'collection', None)
+        self.collection = collection or parent.collection
         
         #: the file where this item is contained/collected from.
         self.fspath = getattr(parent, 'fspath', None)